Connection switching apparatus, connection switching network control system and connection switching network control method

ABSTRACT

In a communication network including connection switching exchanges such as an ATM, a connection management means is provided in a network management unit of the communication network. A group of logical connections with a fixed group size and consecutive identifiers assigned to the connections is treated as a unit. The number of logical connections in such a group is an integer with power of 2. Logical connections in the communication network and connection identifiers assigned to the logical connections are set up and released in connection setting units each equal to a multiple of the group size in a unitary manner across the whole communication network. A priority level is assigned to each connection setting unit. When logical connections have been set for a plurality of connection setting units sharing the same connection identifiers, logical connections with the shared connection identifiers pertaining to a connection setting unit with a smallest size is considered to be valid.

BACKGROUND OF THE INVENTION

In general, the present invention relates to a communication networkwhich is built by using connection switching exchanges, such as an ATM(Asynchronous Transfer Mode) device, and a frame relay, each forimplementing a plurality of logical connections on a single logicalconnection line and which is used for switching a plurality of logicalconnections of a plurality of communication lines, while rewritingconnection identifiers in the connection switching exchanges. Moreparticularly, the present invention relates to a connection switchingnetwork control method, a connection switching apparatus and aconnection switching network management unit which are appropriate forimplementing a high-speed and/or reliable large scale IP/(InternetProtocol) network which can easily recover even in the case of errors.

With regard to a connection switching exchange represented by theconventional ATM device and a frame relay, an example of the ATM deviceis described on pages 17 to 23 of a book entitled ‘ATM Network Biblewith Illustrative Diagrams’ published by Ohm Corporation in 1995. FIG. 2is a diagram showing the functions and structure of the conventionalconnection switching exchange in a simple and plain manner. Theconnection switching exchange 1 is connected to terminating nodes, suchas communication terminals and gateways to another network or to otherconnection switching exchanges, each serving as an adjacent apparatusdirectly connected thereto by communication lines 2. In the figure,there are communication lines 2-1 to 2-9. The connection switchingexchange 1 has a function of setting a plurality of logical connections3 through each of the communication lines 2, each for connecting theconnection switching exchange to a directly connected adjacentapparatus. In the figure, there are shown logical connections 3-1-1,3-1-2 and 3-1-3 set up through the communication line 2-1, a logicalconnection 3-8-1 set up through the communication line 2-8 and logicalconnections 3-9-1 and 3-9-2 set up through the communication line 2-9.

The connection switching exchange 1 further has a function of linkingtwo logical connections 3 set in a single communication line 2 or in twocommunication lines 2 to each other. Any two logical connections 3 arelinked to each other by a communication-line control mechanism 8, aswitching-table search mechanism 7, a connection-identifiertransformation mechanism 5 and a switch mechanism 6, which are providedfor each of the communication lines 2, by using a switching table 4provided for each communication line 2 or provided in common to theentire connection switching exchange 1. In the example shown in FIG. 2,the switching table 4, the switching-table search mechanism 7 and theconnection-identifier transformation mechanism 5 form acommunication-line interface 19 for each of the communication lines 2.In the figure, there are shown line interfaces 19-1, 19-2, 19-8 and19-9.

The switching table 4 is a table showing information on each pair oflogical connections to be linked to each other. More particularly, theswitching table 4 shows mapping relations from information oncommunication lines and connection identifiers assigned to the logicalconnections on the input side to information on communication lines usedby logical connections on the output side and connection identifiersassigned to the logical connections on the output side, as well asinformation on attributes of the logical connections, such as bandattributes. In the example shown in FIG. 2, the connection identifiers3-1-1, 3-1-2 and 3-1-3 using the communication line 2-1 on the inputside are associated respectively with the connection identifier 3-8-1using the communication line 2-8 and the connection identifiers 3-9-1and 3-9-2 using the communication line 2-9 on the output side. In thisexample, the switching table 4 is provided individually for each of thecommunication lines 2.

Since a switching table 4 is associated with each communication line 2,information for input-side communication line 2 is not present in theswitching table 4. More particularly, the switching table 4 comprises acolumn 41 showing connection identifiers assigned to input-side logicalconnections, a column 42 showing information on output-sidecommunication lines, a column 43 showing connection identifiers assignedto logical connections using the output-side communication lines shownin the entry of column 42, a column 44 showing logical connectionattributes and a column 45 showing validity bits each indicating whetherthe line entry is valid or invalid.

The configuration of the switching table 4 varies to a certain degree independence on the technique of implementation of a switching-tablesearch mechanism described below. In some cases, a column entry showingconnection identifiers assigned to logical connections usingcommunications lines on the input side is also omitted as is the casewith information on communication lines on the input side. In theswitching table shown in FIG. 2, the column 45 is used for showingvalidity bits each indicating whether the line entry is valid orinvalid. As an alternative, without using the column 45, a special valuecan be used in one of columns 41 - 43 to indicate that the informationon a communication line or a connection identifier assigned to acommunication line in the column entry for the input or output side isinvalid. It should be noted that, in the case of the ATM, the connectionidentifier used in the switching table 4 is a pair of valuesrepresenting a VPI (Virtual Path Identifier) and a VCI (Virtual ChannelIdentifier) respectively.

The communication-line control mechanism 8 is connected to itsrespective communication line 2, and operates to execute input/outputcontrol in accordance with a technique for exchanging physical signalswith the communication line 2. More specifically, the communication-linecontrol mechanism 8 converts data received serially from thecommunication line 2 into certain data packet units. A data packet 60obtained as a result of such conversion is delivered to theconnection-identifier transformation mechanism 5 by way of a signal line51. When the communication-line mechanism 8 receives a data packet 60from the switch mechanism 6 by way of a signal line 57, to be morespecific, a signal line 57-1, 57-2, 57-8 or 57-9, on the other hand, thecommunication-line mechanism 8 serially outputs the data packet 60 tothe communication line 2 in accordance with the established techniquefor exchanging physical signals with the communication line 2.

The connection-identifier transformation mechanism 5 is a mechanism forrewriting connection-identifier information 62 recorded in the header 61of a data packet 60 received by the connection switching exchange 1. Asdescribed above, a data packet 60 received from one of the communicationlines 2 is processed by the communication line control mechanism 8associated with the communication line 2 before being delivered to theconnection-identifier transformation mechanism 5 by way of the signalline 51. Before rewriting connection-identifier information 62 recordedin the header 61 of the data packet 60, the connection-identifiertransformation mechanism 5 first of all stores the data packet 60temporarily and then delivers the connection-identifier information 62recorded in the header 61 of the data packet 60 to the switching-tablesearch mechanism 7 through a signal line 52.

The switching-table search mechanism 7 searches the switching table 4for a specific table entry 40 of the switching table 4 through a signalline 53 by using the connection-identifier information 62 recorded inthe header 61 of the data packet 60 received through the signal line 52and information on a communication line 2 associated with theswitching-table search means 7 as keys. The specific table entry 40obtained as a result of the search is delivered to theconnection-identifier transformation mechanism 5 by way of a signal line54. It should be noted that the specific data may not be found in thetable entry 40 or the specific data may be found invalid. In order todistinguish the status of the search, search-result valid/invalidinformation for indicating whether the specific data delivered throughthe signal line 54 is valid or invalid is also supplied to theconnection-identifier transformation mechanism 5 by way of a signal line55. The search-result valid/invalid information indicates that thespecific data is invalid if the specific data delivered through thesignal line 54 is invalid in case no valid specific data can bedelivered through the signal line 54.

There are a variety of techniques for implementing the switching-tablesearch mechanism 7. One of the techniques is referred to as a direct-mapmethod whereby input information comprising information on thecommunication line 2 and the connection identifier information 62recorded in the header 61 of the data packet 60 are used as indexes asthey are. In another technique known as a hashing method, the inputinformation is used as an input to a hashing function which generates ahashing value to provide for fast lookup for the target table entry. Instill another technique called a contents addressable memory method, thetarget table entry is searched with a special memory, called a contentaddressable memory, which can directly lookup the contents of the memoryusing the input information and can return the information associatedwith the matched contents. As an alternative, a combination of suchtechniques may also be adopted.

When the connection-identifier transformation mechanism 5 receives aresult of a search operation from the switching-table search mechanism7, the connection identifier transformation mechanism 5 checks thesearch result valid/invalid information received by way of the signalline 55. If a result of the checking indicates that the result of thesearch is valid, the connection-identifier transformation mechanism 5replaces the connection-identifier information 62 recorded in the header61 of the data packet 60 with an output-side connection identifier inthe column entry 43 of the matched table entry 40 received as a searchresult through the signal line 54.

The input data packet 60 processed by the connection-identifiertransformation mechanism 5 is supplied to the switch mechanism 6 alongwith information on the output-side communication line 2 in the columnentry 42 of the table entry 40 received as a search result by way of thesignal line 56, to be more specific, a signal line 56-1, 56-2, 56-8 or56-9. The switch mechanism 6 has the function of switching a data packet60 from an input-side communication line 2 to a communication line 2 onthe output side. The data packet 60 received from the input-sidecommunication line 2 is then output by the switch mechanism 6 to asignal line 57, to be more specific, a signal line 57-1, 57-2, 57-8 or57-9, for the output-side communication line 2 determined by theinformation on the output-side communication line 2 received from theconnection-identifier transformation mechanism 5 along with the packetdata. The data packet 60 output to the signal line 57 is then suppliedto the output-side communication line 2 by way of the aforementionedcommunication-line control mechanism 8 associated with the communicationline 2.

In addition, the connection switching exchange 1 also has a controlmechanism 9 connected to the switch mechanism 6 via the signal lines56-0 and 57-0 inside the exchange 1. Each switching table 4 is set inadvance so that a logical connection 82 having a reserved connectionidentifier is connected to the control mechanism 9 through the signalline 56-0. In general, the control mechanism 9 includes a processor forprocessing information. That is to say, the processor executes softwareprograms to accomplish the functions of the control mechanism 9. Thecontrol mechanism 9 includes, among other elements, a connectionsetup/release mechanism 10. The connection setup/release mechanism 10receives a request to set up a new logical connection link or release anexisting logical connection link. Such a request is received by theconnection setup/release mechanism 10 through a logical connection 82with the reserved connection identifier described above. The logicalconnection 82 is used for signaling purposes. Upon receiving such arequest, the connection setup/release mechanism 10 sets or modifies theswitching table 4 through the signal line 58 and, if necessary, furthertransmits the request to set up or release a logical connection to adirectly connected connection switching exchange or to a communicationapparatus by way of a communication line 2.

If the result of the search of the switching table 4 carried out for aninput data packet 60 is invalid, the result is discarded in theconnection-identifier transformation mechanism 5, or theconnection-identifier transformation mechanism 5 specifies the controlmechanism 9 as a logical connection destination line for the input datapacket 60, instead of rewriting the input data packet 60. In this case,the input data packet 60 is transmitted to the switch mechanism 6, whichthen passes on the packet 60 to the control mechanism 9. In the controlmechanism 9, the input data packet 60 is subjected to error processing.

In addition, a network control method adopted in a communication networkincluding the connection switching exchange 1 described above is alsoexplained on pages 111 to 145 of ‘ATM Network Bible with IllustrativeDiagrams’ published by Ohm Corporation in 1995. As techniques toimplement IP/(Internet Protocol) packet communication with the ATM, forexample, there are known methods referred to as LAN emulation and IPover ATM. According to either method, in transmission of an IP datapacket, the existence of a logical connection for a terminating node inthe ATM communication network specified as a destination IP address inthe header of the IP data packet, or the existence of a logicalconnection for a destination terminating node in an ATM communicationnetwork, which will pass on the IP data packet to the destinationterminating node, is checked. If such a logical connection has not beenset up yet, an ATM logical connection to the destination terminatingnode is set, and the IP data packet is transmitted to the logicalconnection. The logical connection is set with communication between theconnection setup/release mechanism and that of a directly connectedconnection switching exchange using the signaling logical connectiondescribed above. Since connection identifiers assigned to the logicalconnections being set are determined by the connection switchingexchanges on the route of the logical connections themselves, ingeneral, a connection identifier at the output-side of a connectionswitching exchange varies from that at the input-side of the connectionswitching exchange as a data packet is transmitted from one exchange toanother.

In the conventional method described above, each time the destination ofIP data packet data changes, processing to set up a logical connectionneeds to be carried out. In addition, in the worst case, the number oflogical connections becomes equal to a value in the order of the secondpower of the number of terminating nodes in the communication network,giving rise to a problem that there are neither enough connectionidentifiers nor enough switching table entries in a large-scale network.In addition, since relations between connection identifiers assigned toinput-side communication lines and connection identifiers assigned tooutput-side communication lines are controlled and stored independentlyin each connection switching exchange, if a failure occurs somewhere inthe communication network, the relations between such connectionidentifiers are lost, raising a problem that it is necessary to ask auser program at a terminating node to set up end-to-end logicalconnections from the beginning.

SUMMARY OF THE INVENTION

As a basic means to solve the problems described above, there isprovided a network management unit in a communication network connectedto connection switching exchanges of the communication network byoperation-control communication lines. The network management unit hasconnection-control information and a connection management means forcontrolling logical connections in the entire communication network in auniform manner. While referring to and updating the connection-controlinformation, the connection management means treats a fixed number oflogical connections having consecutive connection identifiers as a groupof connections. Logical connections in the communication network arethus controlled in a uniform manner as a connection group or a pluralityof connection groups. Even a logical connection passing through aplurality of connection switching exchanges has only one connectionidentifier. A connection switching exchange is requested to set up orrelease logical connections in group units, each of which compriselogical connections having consecutive identifiers as described above.In more detail, each connection switching exchange has a connectionsetup/release mechanism for executing a function to carry out processingto set up and release logical connections in group units in accordancewith a command received from the connection management means employed inthe network management unit by way of the operation-controlcommunication line. In addition, different priority levels are assignedto a plurality of connection groups. If different logical connectionspertaining to a plurality of connection groups with group sizesdifferent from each other in a connection switching exchange share thesame connection identifiers, the group of connections having a smallgroup size is judged to be to a group having a high priority, and onlyconnections having the highest priority are considered valid for theconnection identifiers.

A connection switching exchange which fits the control of logicalconnections set in group units as described above is provided with aswitching mask register, a mask mechanism and a switching-informationtransformation mechanism for the switching table of the connectionswitching exchange to implement switching of a plurality of logicalconnections pertaining to a specified connection group by using oneswitching-table entry. More specifically, contents of the switching maskregister can be set at a value received from the connectionsetup/release mechanism by way of a signal line. The mask mechanism isused to compute an AND value (a logical product) ofconnection-identifier information recorded in the header of an inputdata packet and the contents of the mask register. The logical productoutput by the mask mechanism is supplied to the switching-table searchmechanism and used thereby as a key for searching the switching table.Switching-table entry information obtained as a result of the searchcarried out by the switching-table search mechanism is supplied to theswitching-information transformation mechanism.

The switching-information transformation mechanism transforms anoutput-side connection identifier of the switching-table entryinformation into an output which is computed as follows. First of all, alogical product of data obtained as a result of bit-by-bit inversion ofthe contents of the switching mask register and theconnection-identifier information recorded in the header of the inputdata packet is computed. Then, an OR value (a logical sum) of thelogical product and the output-side connection identifier of theswitching-table entry information obtained as a result of the searchoperation carried out by the switching-table search mechanism iscomputed. The logical Sum is a result of the processing output producedby the switching-information transformation mechanism. The result of theprocessing output produced by the switching-information transformationmechanism is supplied as a new search result to theconnection-identifier transformation mechanism which implements theconnection switching in conjunction with the switch mechanism.

In addition, in order to implement priority control of a plurality ofgroup units, a set of means comprising the switching table, theswitching mask register, the switching-table search mechanism, the maskmeans and the switching-information transformation mechanism is used asa grouped-search mechanism. A connection switching exchange thus has aplurality of grouped-search mechanisms for carrying out searchoperations for a plurality of groups at the same time. Different fixedpriority levels are further assigned to the plurality of grouped-searchmechanisms or a priority judgment/selection mechanism is provided fordetermining which grouped-search mechanism has the highest priority bycomparing the contents of the switching registers thereof. To be morespecific, in case a plurality of switching-table entries are obtained asa result of simultaneous search operations, a switching-table entry thatis valid and has the highest priority, as indicated by the smallestgroup size, is selected and supplied as a new search result to theconnection-identifier transformation mechanism, which implements theconnection switching in conjunction with the switch mechanism.

In addition to the basic means for solving the problems described above,in order to implement connection switching exchanges of high-speed IPdata packets in a large-scale communication network and to realize areliable network, the following means are used.

First of all, a one-directional interterminal logical connection is setup between every two terminating nodes at an initial setting. Aone-directional interterminal logical connection has a connectionidentifier for each destination terminating node, which is unique to thenode to which the identifier is assigned. Thus, one-directionalinterterminal logical connections from terminating nodes to the samedestination terminating node all have the same connection identifier,forming so-called multipoint-to-point logical connections. Terminatingnodes in a communication network are put in a category of level-0apparatuses and an edge connection switching exchange directly connectedto a terminating node is put in a category of level-1 apparatuses. Aconnection switching exchange directly connected to an apparatus atlevel 1 but not pertaining to the categories of level-1 apparatuses andlevel-0 apparatuses is placed in a category of level-2 apparatuses. Inthe same way, a connection switching exchange directly connected to anapparatus at level (n−1) but not pertaining to the categories oflevel-(n−1) apparatuses and numerically-lower-than-(n−1)-levelapparatuses is placed in a category of level-n apparatuses.

As described above, all terminating nodes of the communication networkare placed in a category of level-0 apparatuses, the lowest level layerin a hierarchy. In such a hierarchy, for apparatuses at all hierarchicallevels i where i>=1, one-directional interterminal logical connectionsfrom an apparatus at level i to apparatuses at level (i−1) haveconsecutive connection identifiers. In addition, for anticipated futureexpansion of apparatus connections, a proper number of extra connectionidentifiers are reserved for apparatuses at level i. Thus, the totalnumber of one-directional interterminal logical connections from anapparatus at level i to apparatuses at level (i−1), including thereserved ones, is made equal to a multiple of a group unit, and theconnection identifiers for the logical connections are assigned in thegroup unit.

A group of logical connections having connection identifiers assignedthereto are set in the group unit from all apparatuses at level (i+1)directly connected to the apparatus at level i to the apparatus at leveli. At a connection switching exchange at level i, a group of logicalconnections from apparatuses at level (i+1) to an apparatus at level iare distributed so as to be connected to logical connections or a groupof logical connections from the apparatus at level i to apparatuses atlevel i−1. In addition, in order to setup meshed interterminalconnections, one-directional logical connections are connected from eachterminating node to the logical connections, which are set in groupunits from high to low hierarchical layers, as described above, in aconnection-group unit equal to or greater than that for the connectionsfrom high to low layers.

Next, as means for implementing connection switching exchanges ofhigh-speed IP data packets, a one-directional interterminal logicalconnection set up at the initial setting described above is used, and,furthermore, each edge connection switching exchange, that is, aconnection switching exchange directly connected to a terminating node,is provided with an IP/connection transformation mechanism as a controlmechanism. The IP/connection transformation mechanism transforms an IPaddress into a connection identifier of a one-directional interterminallogical connection toward a destination terminating node to which IPdata having the IP address is to be transferred. By resorting toIP/connection transformation information distributed by the networkmanagement unit to show a relation between the IP address and theconnection identifier assigned to a one-directional interterminallogical connection toward the destination terminating node, theIP/connection transformation mechanism transmits the IP data packet,received from the origin terminating node, to the destinationterminating node using the connection identifier assigned to theone-directional interterminal logical connection toward the destinationterminating node. As an alternative, the IP/connection transformationmechanism at an edge connection switching exchange gets the destinationIP address from the origin terminating node, transforms the IP addressinto a connection identifier assigned to a one-directional interterminallogical connection toward the destination terminating node, and returnsthe connection identifier assigned to the one-directional interterminallogical connection to the origin terminating node. Then, the originterminating node stores a pair of the returned connection identifier andthe IP address in a cache, and transmits the IP data packet to thedestination terminating node by using the returned connectionidentifier.

Next, as a processing means to process a request to set up or release anew logical connection made dynamically by a terminating node, each edgeconnection switching exchange directly connected to the terminating nodehas terminal-connection-control information to maintain the informationon the logical connections dynamically set or released and theassignment status of the connections indicating whether each connectionis assigned to a terminating node or not. The dynamic connections areset and released in a new-connection-setting unit, which is a multipleof a group unit. Referring to and updating theterminal-connection-control information, the connection setup/releasemechanism buffers requests to setup and release logical connectionsreceived from terminating nodes, and carries out processing to set upand release logical connections in the aforementionednew-connection-setting unit. More particularly, for each request to seta logical connection described above, a group of logical connectionsfrom the edge connection switching exchange to a destination apparatusspecified in the request is set in the aforementionednew-connection-setting unit if an appropriate unassigned connectionmatching the request is not left at the edge connection switchingexchange. In this case, terminal-connection-control information iscreated for the newly set logical connections, and the logicalconnections are marked as free unassigned connections. That is, thecollection of terminal-connection-control information provides theinformation for an unassigned connection buffer pool. Then, a freeunassigned logical connection, which connects the edge connectionswitching exchange and the destination apparatus, is selected from theunassigned connection buffer pool.

The selected logical connection is extended to connect to theterminating node, which issued the request, by setting a switching tableof the edge connection switching exchange with the connection identifierassigned to the selected logical connection. When a request to release alogical connection is received from a terminating node, thecorresponding terminal-connection-control information is updated so thatthe released logical connection is marked as a free unassignedconnection. That is, the released logical connection is considered to beput back into the free unassigned buffer pool. In more detail, theswitching table setting for a part of the logical connection between theconnection switching exchange and the terminating node issuing therequest is invalidated, and the remaining part of the logical connectionfrom the connection switching exchange to the destination apparatus ismarked as a free unassigned connection. In addition, theterminal-connection-control information includes time-out informationfor timing the release of a group of logical connections controlled bythe control information. If all logical connections in a groupcontrolled by terminal-connection-control information has beencontinuously in an unassigned state for a predetermined period of time,the group of logical connections will be released by the connectionsetup/release mechanism, which checks the states of the logicalconnections periodically.

The following is a description of processing to handle a failureoccurring in the communication network by using a plurality of groupsizes. For a group of logical connections corresponding to a unit for anormal communication route, a group of logical connections for a detourcommunication route having the same connection identifiers as the groupof normal logical connections is provided. The group of logicalconnections for a detour communication route has a group size largerthan that of the group of normal logical connections.

In the event of a failure occurring in the communication network, thegrouped-connection management means employed in the network managementunit issues a request to the connection switching exchange on thefailing communication route to carry out processing to invalidate thesetting of the switching of the failing group of logical connectionswith a smaller group size, provided that a group of logical connectionsfor a detour communication route has been set.

If a failure is detected in a portion for which such a group of logicalconnections for a detour communication route is not set, on the otherhand, the grouped-connection management means refers toconnection-control information and information on a configuration oflogical connections among apparatuses in the communication networkstored in the network management unit in order to determine a detourcommunication route. In this case, taking conditions such as acommunication bandwidth into consideration, the grouped-connectionmanagement means forms a judgment as to whether connection identifiersof the failing group of logical connections are to be used as connectionidentifiers of the detour communication route as they are or otherconnection identifiers for the detour communication route are to beused. If necessary, connection identifiers for the detour route are thusassigned.

The grouped-connection management means then carries out processing tomake connection requests to connection switching exchanges orterminating nodes along the detour communication route in the followingorder, in order to setup logical connections between the group oflogical connections for a detour communication route and the group oflogical connections originally connected to the failing logicalconnection or in order to setup the group of logical connections for adetour communication route having connection identifiers for the detourroute in a group unit of the failing group of logical connections. Theprocessing begins with connection switching exchanges in the middle ofthe detour communication route to be followed by a terminating node onthe source side of the detour communication route or at either end ofthe detour communication route if the failing logical connection is abi-directional logical connection. The processing ends with aterminating node at the other end of the detour communication route.

According to the means described above, since a logical connectionalready set between terminating nodes is used, processing to set alogical connection at each IP-packet switching time is not required,allowing switching of a high-speed IP data packet to be carried out. Inaddition, since logical connections controlled in the aforementionedgroup units across the network are used, and grouped logical connectionsare hierarchically connected or distributed relative to each other,connection identifiers are required only in the order of a number ofterminating nodes even if meshed logical connections are set betweenterminating nodes.

Moreover, in the connection switching exchange provided by the presentinvention, since switching of a plurality of logical connections can becarried out by using only one entry of a switching table, functions ofthe connection switching exchange can be utilized effectively withcontrol of the aforementioned group units, allowing meshed logicalconnections between terminating nodes to be implemented by using onlyvery few entries of the switching table. On top of that, even in theconfiguration of a large-scale network, the number of chances thatconnection identifiers and switching-table entries become insufficientbecomes smaller, making an application to a large-scale networkpossible.

In addition, by using a plurality of different group sizes, a group oflogical connections for a detour communication route can be set. With agroup of logical connections for a detour communication route set inadvance, processing to handle a failure can be carried out by merelyinvalidating the failing group of logical connections. Furthermore, evenif a group of logical connections for a detour communication route doesnot exist, a detour route can be easily set with a group unit becauseall logical connections in the communication network are controlled ingroup units by using unique connection identifiers. As a result, areliable network can be constructed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described by referring tothe following diagrams wherein:

FIG. 1 is a block diagram showing an overall configuration of anembodiment implementing control of logical connections in group unitsprovided by the present invention;

FIG. 2 is a block diagram showing a typical configuration of theconventional connection switching exchange;

FIG. 3 is a diagram showing a typical configuration ofconnection-control information used in the control of logicalconnections in group units provided by the present invention;

FIG. 4 is a flow diagram showing a typical processing procedure to setup logical connections in group units provided by the present invention;

FIG. 5 is a flow diagram showing a typical processing procedure torelease logical connections in group units provided by the presentinvention;

FIG. 6 is a flow diagram showing a typical processing procedure to setup or release logical connections for a plurality of group unitsprovided by the present invention;

FIG. 7 is a schematic block diagram showing a typical configuration of aconnection switching exchange suited for the control of logicalconnections in group units provided by the present invention;

FIG. 8 is a flow diagram showing a procedure provided by the presentinvention for processing an input data packet received by the connectionswitching exchange shown in FIG. 7;

FIG. 9 is a schematic block diagram showing a typical configuration of aconnection switching exchange suited for the control of logicalconnections for each plurality of group units provided by the presentinvention;

FIG. 10 is a schematic block diagram showing a typical configuration ofa priority judgment/selection mechanism of the present invention forselecting one out of two results employed in the connection switchingexchange shown in FIG. 9;

FIG. 11 is a block diagram showing an extended configuration of thepriority judgment/selection mechanism of the present invention shown inFIG. 10 for selecting one out of n results;

FIG. 12 is a block diagram showing a procedure provided by the presentinvention for processing an input data packet received by the connectionswitching exchange shown in FIG. 9;

FIG. 13(a) is a flow diagram showing a typical procedure forinitialization of priority processing (process 124) provided by thepresent invention for a plurality of group units carried out by usingthe connection switching exchange provided by the present invention, andFIG. 13(b) is a flow diagram showing a typical procedure of connectionsetup/release processing of the priority processing;

FIG. 14 is a flow diagram showing a typical procedure for connectionsetup/release processing of the priority processing (process 124)provided by the present invention for a plurality of group units carriedout by using the conventional connection switching exchange;

FIG. 15 is a diagram showing a partial configuration of one-directionallogical connections between terminating nodes using logical connectionscontrolled in group units in accordance with the present invention;

FIG. 16 is a flow diagram showing a typical processing procedureprovided by the present invention to set up a one-directional logicalconnection between terminating nodes using logical connectionscontrolled in group units in accordance with the present invention;

FIG. 17 is a flow diagram showing a typical processing procedureprovided by the present invention to hierarchically classify apparatusesin a communication network as part of the processing shown in FIG. 16;

FIG. 18 is a flow diagram showing a typical processing procedureprovided by the present invention to assign one-directional logicalconnections to the same branch tree as part of the processing shown inFIG. 16;

FIG. 19 is a diagram showing another partial configuration ofone-directional logical connections between terminating nodes usinglogical connections controlled in group units in accordance with thepresent invention;

FIG. 20 is a schematic block diagram showing a typical techniqueprovided by the present invention to transmit IP data packets throughone-directional logical connections between terminating nodes usinglogical connections controlled in group units in accordance with thepresent invention;

FIG. 21 is a flow diagram showing a typical procedure for initializationof the technique provided by the present invention to transmit IP datapackets through one-directional logical connections between terminatingnodes using logical connections controlled in group units in accordancewith the present invention shown in FIG. 20;

FIG. 22 is a flow diagram showing a typical transmission procedure forthe technique provided by the present invention to transmit IP datapackets through one-directional logical connections between terminatingnodes using logical connections controlled in group units in accordancewith the present invention shown in FIG. 20;

FIG. 23 is a schematic block diagram showing another typicalconfiguration of a communication network provided by the presentinvention to transmit IP data packets through one-directional logicalconnections between terminating nodes using logical connectionscontrolled in group units in accordance with the present invention;

FIG. 24 is a flow diagram showing a typical transmission procedure totransmit IP data packets through one-directional logical connectionsbetween terminating nodes using logical connections controlled in groupunits adopted by the communication network shown in FIG. 23 inaccordance with the present invention;

FIG. 25 is a schematic block diagram showing the configuration of anembodiment adopting still another typical technique provided by thepresent invention to transmit IP data packets through one-directionallogical connections between terminating nodes using logical connectionscontrolled in group units in accordance with the present invention;

FIG. 26 is a flow diagram showing a typical procedure for initializationof the technique adopted by the embodiment shown in FIG. 25 to transmitIP data packets through one-directional logical connections betweenterminating nodes using logical connections controlled in group units inaccordance with the present invention;

FIG. 27 is a flow diagram showing a typical transmission procedure forthe technique adopted by the embodiment shown in FIG. 25 to transmit IPdata packets through one-directional logical connections betweenterminating nodes using logical connections controlled in group units inaccordance with the present invention;

FIG. 28 is a diagram showing a typical configuration of terminalconnection information used for setting up and releasing logicalconnections controlled in group units in accordance with the presentinvention;

FIG. 29 is a flow diagram showing a typical procedure for processing arequest to set up a logical connection made by a terminating node usinglogical connections set in group units in accordance with the presentinvention;

FIG. 30 is a flow diagram showing a typical procedure for processing arequest to release a logical connection made by a terminating node usinglogical connections controlled in group units in accordance with thepresent invention;

FIG. 31 is a flow diagram showing a typical processing procedure torelease a group of logical connections set up in group units which iscarried out periodically as part of the processing to process a requestto release a logical connection shown in FIG. 30 in accordance with thepresent invention;

FIG. 32 is a diagram showing an example of a technique to recover afailure by using a set of logical connections controlled in group unitsin accordance with the present invention;

FIG. 33 is a diagram showing an example of another technique to recovera failure using a set of logical connections controlled in group unitsin accordance with the present invention;

FIG. 34 is a flow diagram showing typical techniques in a processingprocedure to recover a failure using a set of logical connectionscontrolled in group units in accordance with the present invention shownin FIGS. 32 and 33;

FIG. 35 is a schematic block diagram showing a typical configuration ofan operation-control communication line using logical connections in acommunication network in accordance with the present invention; and

FIG. 36 is a schematic block diagram showing a typical configurationprovided by the present invention to include control mechanisms ofconnection switching exchanges for communication lines.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will become more apparent from a careful study ofthe following detailed description of some preferred embodiments withreference to the accompanying drawings.

FIG. 1 is a diagram showing the overall configuration of an embodimentimplementing control of logical connections in group units provided bythe present invention. As shown in the figure, the communication networkprovided by the present invention has a configuration comprising aplurality of terminating nodes and a plurality of relay apparatusesconnected to each other by communication lines. The terminating nodesare communication terminal apparatuses and gateways connected toexternal networks, whereas the relay apparatuses are connectionswitching exchanges. The typical configuration shown in the figureincludes communication terminal apparatuses 11-1, 11-2, 11-3, 11-4,11-6, 11-7 and 11-8, a gateway 11-9 connected to an external network 12and connection switching exchanges 1-1, 1-2, 1-3, 1-4, 1-10 and 1-11.The communication network is also provided with a network managementunit 13 for controlling the entire communication network. The networkmanagement unit 13 is connected to all the connection switchingexchanges 1 by an operation-control network 14 provided separately fromthe communication lines 2. The operation-control network 14 is providedin the form of operation-control communication lines 15 for exchanginginformation including requests to set up and release a logicalconnection between the network management unit 13 and the connectionswitching exchanges 1.

In the network management unit 13, network-configuration information 20concerning the communication network is stored. The network managementunit 13 has a network-configuration-information setting means 17 forsetting and updating the network-configuration information 20. As shownin the figure, the network-configuration-information setting means 17 iscapable of communicating with an external apparatus through acommunication line 16, which is connected to the network controlmanagement unit 13, in addition to the operation-control communicationlines 15. The network-configuration information 20 includes information21 on the configuration of logical connections between the terminatingnodes 11 and the connection switching exchanges 1 of the communicationnetwork, initial connection setting specifying information 22, that is,initial connection setting information, and group control specifyinginformation 23. The group control specifying information 23 is composedof a group size 24 indicating a fixed unit used for controlling andsetting up logical connections and group applicable range information 25specifying a range of connection identifiers to which control in groupunits is applied.

The network management unit 13 further has a grouped-connectionmanagement means 18. In accordance with the group control specifyinginformation 23 stored as part of the network-configuration information20, the grouped-connection management means 18 controls logicalconnections having connection identifiers specified by the groupapplicable range information 25 of the group control specifyinginformation 23 in units specified by the group size 24 of the groupcontrol specifying information 23, and stores results of the control asconnection-control information 30. FIG. 3 is a diagram showing anembodiment of the connection-control information 30. As shown in thefigure, as control information of all logical connections in a group,the connection-control information 30 comprises a copy 35 of the groupcontrol specifying information 23 and information 36 associating thegroup with a switching table, as will be described later. The logicalconnection control 30 also includes a state of utilization 31 of a groupof logical connections, information on routes 32 and information onattributes 33 for each group of logical connections with a sizespecified by the group size 24.

FIG. 4 is a diagram showing a typical processing procedure carried outby the grouped-connection management means 18 provided by the presentinvention to set up logical connections in group units specified by thegroup size 24. As shown in the figure, the procedure begins with aprocess 101 in which the grouped-connection management means 18 startsthe work to set up logical connections when setting up initial logicalconnections in accordance with the initial connection setting specifyinginformation 22 stored in the network management unit 13, or whenreceiving a request to set up new logical connections from the edgeconnection switching exchange 1-1, 1-2, 1-3 or 1-4, directly connectedto one of the terminating nodes 11, by way of the operation-controlcommunication line 15.

The flow of the procedure then goes on to a process 102 in which thegrouped-connection management means 18 assigns a batch of freeconsecutive connection identifiers or connection identifiers specifiedby the initial connection setting specifying information 22 or specifiedin a request to set up a logical connection by referring to theconnection-control information 30 with the group size 24 of the groupcontrol specifying information 23 used as a unit.

Then, the flow of the procedure proceeds to a process 103 in which thegrouped-connection management means 18 identifies connection switchingexchanges 1 on a specified connection route by referring to theconnection-configuration information 21 stored in the network managementunit 13. Subsequently, the flow of the procedure continues to a process104 in which the grouped-connection management means 18 gives a commandto the connection switching exchanges 1 on the specified connectionroute identified in the process 103 through the operation-controlcommunication lines 15 to set up a group of logical connections so as tocarry out switching of a batch of logical connections from inputcommunication lines to output communication lines on the requested routeby using the same consecutive connection identifiers assigned to theinput and output communication lines in the process 102.

The flow of the procedure then goes on to a process 105 in which, ineach of the connection switching exchange systems 1 receiving thecommand in the process 104, the connection setup/release mechanism 10employed in the connection switching exchanges 1 receives the commandand sets up the switching table 4 in a batch operation so as to carryout the switching of the logical connections in the specified group oflogical connections from the specified input communication lines to thespecified output communication lines by using the specified connectionidentifiers as they are without modifying the values of the connectionidentifiers.

In the process 105, an indication of a successful or unsuccessful resultof the logical connection setting is returned to the grouped-connectionmanagement means 18 by way of one of the operation-control communicationlines 15. Finally, the flow of the procedure continues to a process 106in which the grouped-connection management means 18 receives theindication of the successful or unsuccessful result of the logicalconnection setting-up operation carried out in the process 105 from eachof the connection switching exchanges 1 and updates theconnection-control information 30 in accordance with the obtainedresult, completing the processing to set up the logical connections.

FIG. 5 is a diagram showing a typical processing procedure carried outby the grouped-connection management means 18 provided by the presentinvention to release logical connections in group units specified by thegroup size 24. As shown in the figure, the procedure begins with aprocess 111 in which the grouped-connection management means 18 startsprocessing to release logical connections of a group unit when thegrouped-connection management means 18 receives a request to releaselogical connections of the group unit from any of the edge connectionswitching exchanges 1-1, 1-2, 1-3 and 1-4 directly connected to theterminating nodes 11 by way of the operation-control communication lines15, or when it becomes necessary to release a logical connection in theevent of a change in initially set up logical connections due to achange in configuration, a failure or an abnormality.

The flow of the procedure then goes on to a process 112 in which thegrouped-connection management means 18 identifies connection switchingexchanges 1 on a route of a portion to be released, that is, a routeinvolving logical connections to be released, by referring to theconnection-control information 30 stored in the network management unit13.

Then, the flow of the procedure proceeds to a process 113 in which thegrouped-connection management means 18 gives a command to the connectionswitching exchanges 1 on the route identified in the process 112 torelease the logical connections of the group unit created in theprocessing to set up the logical connections in a batch operation.

Subsequently, the flow of the procedure continues to a process 114 inwhich, in each of the connection switching exchanges 1 receiving thecommand in the process 113, the command is received by the connectionsetup/release mechanism 10 employed by the connection switching exchange1 and the connection setup/release mechanism 10 clears an entry in theswitching table 4 of the connection switching exchange 1 correspondingto the specified group of logical connections in a batch operation,returning an indication of a successful or unsuccessful result of theoperation to the grouped-connection management means 18 by way of one ofthe operation-control communication lines 15.

Finally, the flow of the procedure continues to a process 115 in whichthe grouped-connection management means 18 receives the indication ofthe successful or unsuccessful result of the logical connectionreleasing operation carried out in the process 114 from each of theconnection switching exchanges 1 and updates the connection-controlinformation 30 in accordance with the obtained result, completing theprocessing to release the logical connections.

For the sake of simplicity, network-wide control methods to set up andrelease logical connections in only a group unit have been explainedabove. In the following description, on the other hand, network-widecontrol methods to set up and release logical connections in a pluralityof group units will be explained.

In the first place, in the network management unit 13 shown in FIG. 1, aplurality of pieces of group control specifying information 23 arestored as part of the network-configuration information 20. The groupsize 24 in one of the same plurality of pieces of group controlspecifying information 23 is a multiple or a fraction of the group size24 in another piece of the group control specifying information 23. Inaddition, for each of the same plurality of pieces of group controlspecifying information 23, the grouped-connection management means 18employed by the network management unit 13 stores individualconnection-control information 30 in the network management unit 13.

FIG. 6 is a diagram showing a typical processing procedure carried outby the grouped-connection management means 18 provided by the presentinvention to set up or release logical connections for a plurality ofgroup units. As shown in the figure, the procedure begins with a process121 in which processing to set up or release logical connections isstarted in accordance with what is described for the process 101 or 111.The grouped-connection management means 18 receives a command or arequest to set up or release logical connections. The command or requestis a command or request that explicitly indicates which piece of groupcontrol specifying information 23 is to be used. As an alternative, thegrouped-connection management means 18 receives an implicit command orrequest that indicates which piece of group control specifyinginformation is to be used as implicitly suggested by a relation betweena specified connection identifier and a piece of group controlspecifying information to be used.

The flow of the procedure then goes on-to a process 122 in which thepiece of group control specifying information 23 to be used in thefollowing processing and the connection-control information 30associated with the piece of group control specifying information 23 arethen selected. Then, the flow of the procedure proceeds to a process 123in which the processes 102 and 103 are carried out to prepare forsetting-up of logical connections or the process 112 is performed toprepare for a release of logical connections by using the group controlspecifying information 23 and the connection-control information 30selected in the process 122.

Subsequently, the flow of the procedure continues to a process 124 inwhich the process 104 is carried out to give a command to involvedconnection switching exchanges 1 identified in the process 103 to set uplogical connections of specified group units, or the process 113 isperformed to give a command to the involved connection switchingexchanges 1 identified in the process 112 to release logical connectionsof specified group units. In this case, however, all the pieces ofconnection-control information 30 are checked. If logical connections ina plurality of group units have to be set up for the same connectionidentifiers or if logical connections of a plurality of group unitsalready set up for the same connection identifiers have to be released,that is, if logical connections are observed in ranges with connectionidentifiers overlapping a plurality of group units, thegrouped-connection management means 18 identifies a group unit havingthe smallest group size among the plurality of group units in the rangeswith the overlapping connection identifiers as a valid group unit to beprocessed.

The flow of the procedure then goes on to a process 125 in which eachof-the connection switching exchanges 1 receiving a command in theprocess 124 updates the switching table 4 in the connection switchingexchange 1 and sets up or releases logical connections in a batchoperation, returning an indication of a successful or unsuccessfulresult of the operation to the grouped-connection management means 18employed in the network management unit 13 by way of one of theoperation-control communication lines 15 in accordance with the commandin the same way as the process 105 or 114 respectively.

Finally, the flow of the procedure continues to a process 126 in whichthe grouped-connection management means 18 receives the indication ofthe successful or unsuccessful result of the logical connectionsetting-up or releasing operation carried out in the process 125 fromeach of the connection switching exchanges 1 and updates theconnection-control information 30 selected in the process 122 inaccordance with the obtained result in the same way as the process 106or 115, completing the processing to set-up or release the logicalconnections, respectively.

It should be noted that an embodiment implementing a method to carry outprocessing in the process 124 in case a specified connection identifieroverlaps a plurality of group units will be described later.

Other embodiments of the present invention will be explained withreference to FIGS. 7 and 8. FIG. 7 is a diagram showing a typicalconfiguration of a connection switching exchange suited for the controlof logical connections in group units provided by the present invention,and FIG. 8 is a diagram showing a procedure provided by the presentinvention for processing an input data packet received by the connectionswitching exchange shown in FIG. 7.

As shown in FIG. 7, the embodiment implementing the connection switchingexchange 1 also includes a switching mask register 46, a mask mechanism47 and a switching-information transformation mechanism 48 provided forthe switching table 4, in addition to the components of the conventionalconnection switching exchange shown in FIG. 2. The switching maskregister 46 is used for setting a value received from the connectionsetup/release mechanism 10 through a signal line 58. In the embodimentshown in FIG. 7, the switching mask register 46, the mask mechanism 47,the switching-information transformation mechanism 48 and the switchingtable 4 constitute a communication line interface 19 provided for eachcommunication line 2. In the figure, communication line interfaces 19-1and 19-2 for communication lines 2-1 and 2-2, respectively, are shown.The control mechanism 9 is connected to an operation-controlcommunication line 15 which is a part of an operation-control network14. The connection setup/release mechanism 10 employed in the controlmechanism 9 receives a command to set up or release logical connectionsfrom the network management unit 13 shown in FIG. 1 by way of theoperation-control communication line 15. A flow of data experiencingconnection switching carried out by the connection switching exchange 1is described with reference to FIG. 8 as follows.

As shown in FIG. 8, the flowchart begins with a process 131 in whichdata received serially from the communication line 2, that is, thecommunication line 2-1 or 2-2, is converted into data-packet units bythe communication control mechanism 8 connected to the communicationline 2. The input data packet 60 is delivered to theconnection-identifier transformation mechanism 5 through the signal line51. The flow of the connection-switching procedure then goes on to aprocess 132 in which, first of all, the connection-identifiertransformation mechanism 5 receiving the data packet 60 temporarilystores the packet 60 and outputs information on connection identifiers62 recorded in the header 61 of the packet 60 to a signal line 52 a. Inthe case of the conventional connection switching exchange, the signalline 52 a is directly connected to the switching-table search mechanism7. In the case of the connection switching exchange 1 provided by thepresent invention, on the other hand, the signal line 52 a is connectedto the corresponding mask mechanism 47.

In a process 133 following the process 132, the mask mechanism 47computes the logical product (the AND value) of the information onconnection identifiers 62 included in the input data packet 60 receivedfrom the signal line 52 a and the contents of the switching maskregister 46 supplied to the mask mechanism 47 by way of a signal line59, and supplies the logical product to the switching-table searchmechanism 7 through a signal line 52 b.

Then, the flow of the connection-switching procedure proceeds to aprocess 134 in which the switching-table search mechanism 7 searches theswitching table 4 through a signal line 53 on the basis of theinformation on connection identifiers 62 in the input data packet 60,which is supplied thereto by way of the signal line 52 b and hascompleted the mask processing, and communication-line information isprovided on the communication line 2 corresponding to theswitching-table search mechanism 7 in the same way as the conventionalconnection switching exchange. As a result of the search operation, aswitching-table entry 40 and search-result valid/invalid informationindicating whether the entry 40 is valid or invalid are output,respectively, to signal lines 54 a and 55 connected to theswitching-table search mechanism 7. In the case of the conventionalconnection switching exchange, the signal line 54 a is connecteddirectly to the connection-identifier transformation mechanism 5. In thecase of the connection switching exchange 1 provided by the presentinvention, on the other hand, the signal line 54 a is connected to theswitching-information transformation mechanism 48.

Subsequently, the flow of the connection-switching procedure continuesto a process 135 in which the switching-information transformationmechanism 48 computes a logical product of the information on connectionidentifiers 62 of the input data packet 60 supplied thereto by way ofthe signal line 52 b and a value resulting from bit-by-bit inversion ofthe contents of the switching mask register 46 which are supplied to theswitching-information transformation mechanism 48 by way of the signalline 59.

Then, the switching-information transformation mechanism 48 computes alogical sum (an OR value) of the logical product and information onoutput-side connection identifiers 43 included in the switching-tableentry 40 of the search result supplied thereto by way of the signal line54 a, and outputs the logical sum to a signal line 54 b. The signal line54 b is connected to the connection-identifier transformation mechanism5 and the processing carried out thereafter is the same as theconventional connection switching exchange. More particularly, the flowof the connection-switching procedure goes on to a process 136 in whichthe connection-identifier transformation mechanism 5 receives thesearch-result valid/invalid information from the signal line 55 and aresult of the search operation completing the transformation in theswitching-information transformation mechanism 48 from the signal line54 b.

If the result of the search operation is valid, the information onconnection identifiers 62 of the input data packet 60 is changed to theinformation on output-side connection identifiers 43 of the searchresult completing the transformation. Then, the input data packet 60,along with rewritten connection identifiers and output communicationline information 42 of the switching-table entry 40 obtained as a resultof the search operation, is transferred to the switch mechanism 6 by wayof a signal line 56, that is, a signal line 56-1 or 56-2 shown in FIG.7. If the result of the search operation is invalid, on the other hand,the result is discarded by the connection-identifier transformationmechanism 5, or the input data packet 60 is transferred to the switchmechanism 6 by specifying the control mechanism 9 as outputcommunication line information without rewriting the input data packet60.

Subsequently, the flow of the connection-switching procedure goes on toa process 137 in which the switch mechanism 6 passes on the rewrittendata packet 60 received from the signal line 56 to the correspondingcommunication control mechanism 8 through a signal line 57, that is, asignal line 57-1 or 57-2, corresponding to the communication line 2 ofthe destination of the connection switching indicated by the outputcommunication line information 42 which was received also from thesignal line 56. Finally, the flow of the connection-switching procedurecontinues to a process 138 in which the communication control mechanism8 serially outputs the rewritten data packet 60 received from the signalline 57 to the communication line 2 connected to the communicationcontrol mechanism 8. It should be noted that, in the case of an invalidsearch-operation result not discarded by the connection-identifiertransformation mechanism 5, as a result of the connection switching, theswitch mechanism 6 transmits the data packet 60 to the control mechanism9 for carrying out error processing on the data packet 60.

As described above, in this embodiment implementing a connectionswitching exchange wherein, through the use of a value masked by aswitching mask register as a unit, a group of logical connections havingconsecutive connection identifiers in the unit can be subjected toconnection switching by using only one entry of a matching table. Inbrief, the embodiment implements connection switching on logicalconnections in a group unit. The following is a description of anembodiment for carrying out connection switching on logical connectionsof a plurality of group units.

FIG. 9 is a diagram showing an embodiment implementing a typicalconfiguration of a connection switching exchange suited for the controlof logical connections for each plurality of group units provided by thepresent invention. FIG. 12 is a diagram showing a procedure provided bythe present invention for carrying out connection switching on an inputdata packet received by the connection switching exchange shown in FIG.9. This embodiment and the procedure will be explained in the same wayas the previous embodiment.

In the case of the embodiment shown in FIG. 7, only 1 set of theswitching table 4, the switching mask register 46, the mask mechanism 47and the switching-information transformation mechanism 48 is providedfor each communication line 2. In the case of the embodiment shown inFIG. 9, on the other hand, the switching table 4, the switching maskregister 46, the mask mechanism 47 and the switching-informationtransformation mechanism 48 are part of a set referred to as agrouped-search mechanism 50, and a plurality of grouped-searchmechanisms 50-1, 50-2 and so on are provided for each communication line2. In addition, in the present embodiment, a priority judgment/selectionmechanism 49 is newly provided for each communication line 2.

As shown in FIG. 12, the procedure begins with a process 141 in whichdata received serially from a communication line 2, that is, any of thecommunication lines 2-1, 2-2 and so on, is subjected to the processes131 and 132 in the communication line control mechanism 8 and theconnection-identifier transformation mechanism 5, respectively, and theinformation on connection identifiers 62 included in the input datapacket 60 is output to the signal line 52 a. The flow of the procedurethen goes on to a process 142 in which the information on connectionidentifiers 62 included in the input data packet 60 received from thesignal line 52 a is delivered simultaneously to the mask mechanisms 47and the switching-information transformation mechanisms 48 employed inthe plurality of grouped-search mechanisms 50 for concurrently carryingout the processes 133, 134 and 135 to search the same plurality ofswitching tables 4 therein in parallel. Final results of the parallelsearch operations are output by the switching-information transformationmechanisms 48 of the grouped-search mechanisms 50 to signal lines 54 b,that is, 54 b-1, 54 b-2 and so on, and pieces of search-resultvalid/invalid information indicating whether the final results are validor invalid are output by the switching-table search mechanisms 7 of thegrouped-search mechanisms 50 to signal lines 55 b, that is, 55 b-1, 55b-2 and so on.

The signal lines 54 b and 55 b are connected to the priorityjudgment/selection mechanism 49 for the communication line 2-1 forselecting one of the above final results obtained from the searchoperations carried out on the switching tables 4 employed in theplurality of grouped-search mechanisms 50. In more detail, in a process143 following the process 142, the priority judgment/selection mechanism49 receives the final results of the search operations, that isswitching-table entries 40 completing transformation in theswitching-information transformation mechanisms 48 of the grouped-searchmechanisms 50, from the signal lines 54 b, and the pieces ofsearch-result valid/invalid information indicating whether the finalresults are valid or invalid are output by the switching-table searchmechanisms 7 of the grouped-search mechanisms 50 from the signal lines55 b. The priority judgment/selection mechanism 49 selects one of thefinal search results from the plurality of grouped-search mechanisms 50which is indicated as a valid switching-table entry 40 by the associatedsearch-result valid/invalid information and has the maximum priority,outputting the selected final search result to a signal line 54 c.

The maximum priority is determined from the values of predeterminedfixed priorities assigned to the grouped-search mechanisms 50 for finalsearch results with the matching-table entries 40 thereof indicated asvalid entries by the pieces of search-result valid/invalid informationassociated with the final search results. As an alternative, the maximumpriority is determined by inputting contents of the switching maskregisters 46 of the grouped-search mechanisms 50 by way of signal lines59, that is, signal lines 59-1, 59-2 and so on, treating the contents asunsigned integers and picking up the greatest unsigned integer as themaximum priority of a switching-table entry 40 obtained as a finalresult of the search operations carried out by the grouped-searchmechanisms 50.

In addition, the priority judgment/selection mechanism 49 also computesthe logical sum (an OR value) of all the pieces of search-resultvalid/invalid information received from the signal lines 55 b at thesame time, and outputs the logical sum to a signal line 55 c assearch-result valid/invalid information indicating whether the selectedfinal result is valid or invalid. The signal lines 55 c and 54 c areconnected to the connection-identifier transformation mechanism 5 forthe communication line 2-1. Processing carried out thereafter is thesame as the conventional connection switching exchange. That is to say,in the final process 144 following the process 143, the information onconnection identifiers of the data packet 60 is rewritten by theconnection-identifier transformation mechanism 5 in the same way as theprocessing 136, connection switching of the data packet 60 amongcommunication lines 2 is carried out by the switch mechanism 6 in thesame way as the process 137 and the data packet 60 is output to acommunication line 2 by the communication-line control mechanism 8 inthe same way as the process 138.

FIG. 10 is a diagram showing a typical configuration of the priorityjudgment/selection mechanism 49 for carrying out the process 143 of theprocedure shown in FIG. 12 to determine a search result with a maximumpriority employed in the connection switching exchange shown in FIG. 9.In this embodiment, a judgment based on a priority in the process 143described above is formed to select one of two search results producedby two grouped-search mechanisms 50.

As shown in FIG. 10, the priority judgment/selection mechanism 49comprises 4 selection circuits 91-1 to 91-4, a comparison circuit 92 andan OR circuit 94. Each of the selection circuits 91 has a select inputhaving a value of0 or 1 and two selectable inputs to be selected. Theselection circuits 91 each have a function to select one of the twoselectable inputs in dependence on whether the value of the select inputis 0 or 1. The comparison circuit 92 has two inputs: input 1 and input 2which are each treated as an unsigned integer. The comparison circuit 92has a function to output a value of 1 for input 1>input 2, or a value of0 for input 1<=input 2. The selection circuits 91-1 and 91-2 receive,respectively, pieces of search-result valid/invalid information 55 b-1and 55 b-2 generated by the 2 grouped-search mechanisms 50 as selectsignals. As the selectable signals, the selection circuit 91-1 receivesthe contents of the switching mask register 59-1 and a value of 0,whereas the selection circuit 91-2 receives the contents of theswitching mask register 59-2 and a value of 0.

With the search-result valid/invalid information 55 b-1 set at 1, theselection circuit 91-1 selects the contents of the switching maskregister 59-1. With the search-result valid/invalid information 55 b-1set at 0, on the other hand, the selection circuit 91-1 selects thevalue of 0. In the same way, with the search-result valid/invalidinformation 55 b-2 set at 1, the selection circuit 91-2 selects thecontents of the switching mask register 59-2. With the search-resultvalid/invalid information 55 b-2 set at 0, on the other hand, theselection circuit 91-2 selects the value of 0. The role played by theselection circuits 91-1 and 912 is to compute the value of a effectivepriority level.

As described above, when the search-result valid/invalid information 55b is set at 0 to indicate an invalid result of a search operation, theselection circuit 91-1 or 91-2 outputs the value of 0 representing theminimum priority level, and a pseudo priority level is assigned to theinvalid result of the search operation. The effective priority levelsoutput by the selection circuits 91-1 and 91-2 are supplied to thecomparison circuit 92. The comparison circuit 92 compares the effectivepriority levels output by the selection circuits 91-1 and 91-2 with eachother, and outputs the result of the comparison to the selection circuit91-3 as a select input.

The selection circuit 91-3 selects either of 2 pieces of search resultinformation 54 b-1 and 54 b-2 output by the grouped-search mechanisms 50to the selection circuit 91-3 in accordance with the result of thecomparison supplied thereto by the comparison circuit 92, and outputsthe selected search result information to the signal line 54 c. Morespecifically, when the effective priority level computed by theselection circuit 91-1 is higher than that of the selection circuit91-2, the search result information 54 b-1 is selected by the selectioncircuit 91-3 and output to the signal line 54 c. Otherwise, the searchresult information 54 b-2 is selected and output to the signal line 54c.

In addition, the effective priority levels output by the selectioncircuits 91-1 and 91-2 are also supplied as selectable inputs, and theresult of the comparison output by the comparison circuit 92 is alsosupplied as a select input to the selection circuit 91-4. The selectioncircuit 91-4 thus selects the higher one between the effective prioritylevels output by the selection circuits 91-1 and 91-2 and outputs theselected priority level to a signal line 93. The priority level conveyedby the signal line 93 is used for selecting one of results output bythree or more grouped-search mechanisms 50 by a judgment on prioritylevels to be described later.

While the processing to form a judgment on priority levels describedabove is being carried out, the pieces of search-result valid/invalidinformation 55 b-1 and 55 b-2 are also supplied to the OR circuit 94 fortaking the logical sum of the pieces of search-result valid/invalidinformation 55 b-1 and 55 b-2. The logical sum is output to the signalline 55 c to indicate whether the result output by the priorityjudgment/selection mechanism 49 to the signal line 54 c is valid orinvalid.

As described above, FIG. 10 is a diagram showing a typical configurationof an embodiment implementing the priority judgment/selection mechanism49 for forming a judgment to determine one of the search results outputby two grouped-search mechanisms 50. On the other hand, FIG. 11 is adiagram showing an extended configuration obtained by building ahierarchical structure of a plurality of priority judgment/selectionmechanisms 49 shown in FIG. 10 for selecting one of the search resultsoutput by three or more grouped-search mechanisms 50. It should be notedthat the embodiment shown in FIG. 11 implements a selection mechanism toselect one of the search results output by four grouped-searchmechanisms 50.

Described next with reference to FIG. 13 is an embodiment implementingprocessing in the process 124 of the procedure shown in FIG. 6, which iscarried out to cope with a connection identifier overlapping a pluralityof group units by using the connection switching exchange provided bythe present invention described with reference to FIGS. 7 to 12. In thepresent embodiment, the process 124 is implemented by the two proceduresshown in FIGS. 13(a) and 13(b). To be more specific, FIG. 13(a) is adiagram showing a procedure for grouped-connection setup/releaseinitialize processing and FIG. 13(b) is a diagram showing a procedurefor postinitialization grouped-connection setup/release requestprocessing.

In the procedure of the grouped-connection setup/release initializeprocessing shown in FIG. 13(a), the grouped-connection management means18 employed in the network management unit 13 gives a command toconnection switching exchanges 1 provided by the present invention, asdescribed with reference to FIGS. 7 to 12, to carry out initializationprior to a command to set up grouped logical connections. The sizes ofthe group units can each be set only to a power of 2, and, in theinitialization, the grouped-connection management means 18 employed inthe network management unit 13 gives a command to the connectionsetup/release mechanisms 10 of the connection switching exchanges 1 ofthe present invention, as described with reference to FIGS. 7 to 12 byway of the operation-control communication lines 15 to carry out aprocess 151 shown in FIG. 13(a).

In the case of a connection switching exchange 1 with a fixed prioritylevel assigned to each of a plurality of grouped-search mechanisms 50, agrouped-search mechanism 50 with higher priority level should beassigned with smaller group size value. The connection setup/releasemechanism 10 of the connection switching exchange 1 is requested to seta value obtained as a result of bit-by-bit inversion (of the groupsize-1) in the switching mask register 46 employed in eachgrouped-search mechanism 50 to which the group size is assigned.

The flow of the procedure then goes on to a process 152 in which thegrouped-connection management means 18 employed in the networkmanagement unit 13 is waiting for responses indicating completion of theinitialization coming from the connection switching exchange 1. Thegrouped-connection management means 18 stores a relation between groupunits and switching tables 4 of the grouped-search mechanisms 50 in theconnection-control information 30 for the group units as information 36associating the group units with the switching tables 4.

As described above, FIG. 13(b) is a diagram showing a procedure forpost-initialization grouped-connection setup/release request processing,a processing carried out after the grouped-connection setup/releaseinitialization shown in FIG. 13(a). As shown in FIG. 13(b), in a process153 of the procedure for post-initialization grouped-connectionsetup/release request processing, by referring to the information 36associating the group units with the switching tables 4 recorded duringthe initialization as part of the connection-control information 30, thegrouped-connection management means 18 gives a command to connectionswitching exchanges 1 to carry out processing to set up or releaselogical connections for a group unit associated with a switching table 4by specifying a grouped-search mechanism 50 for the associated switchingtable 4.

The procedures shown in FIG. 13(a) and 13(b) are provided for acommunication network comprising connection switching exchanges 1provided by the present invention suited for the grouped logicalconnection control provided by the present invention as explained withreference to FIGS. 7, 8, 9 and 10.

On the other hand, FIG. 14 is a diagram showing a typical procedure ofthe process 124 of FIG. 6 carried out by using the conventionalconnection switching exchange having neither a grouped-search mechanism50 nor priority judgment/selection mechanism 49 for a plurality of groupunits with a connection identifier overlapping some of the group units.

With use of the conventional connection switching exchange, first ofall, in a process 161, the grouped-connection management means employedin the network management unit respectively uses values of the entireconnection-identifier space as a range, when setting up logicalconnections initially, and values of a group of connection identifiersof logical connections to be set up or released as a range, when settingup or releasing the logical connections after the initialization. Theend points of the range and the start and end connection identifiers ofall grouped logical connections in the range which have been set up orwill be set up from now on are taken as change points. The change pointsare sorted in an increasing order of change-point values to form a listof change points. The flow of the procedure then goes on to a process162 in which a group size of a request to set up or release logicalconnections is stored as an affected group size.

Then, the flow of the procedure proceeds to a process 163 in which thegrouped-connection management means searches for a logical connectionhaving a connection identifier which is the same as the start pointvalue of the range. If such logical connections exist, the flow of theprocedure continues to a process 164 in which the start point is storedas a set start point, and the smallest group size among the foundlogical connections is stored as a setting group size. The flow of theprocedure then goes on to a process 168. If a logical connection havinga connection identifier which is the same as the start point is notfound in the search carried out in the process 163, on the other hand,the flow of the procedure proceeds to a process 165 in which the valueof the start point is stored as a set end point. The flow of theprocedure then continues to a process 166 to store the next changepoint, which follows the set end point in the change-point list and hasa value different from the set end point, as a set start point. In thecase of a request to release logical connections, a command to release agroup of logical connections having connection identifiers from the setend point to the set start point is given to connection switchingexchanges on a route of the logical connections to be released. Then,the flow of the procedure goes on to a process 167 in which a smallestgroup size among logical connections having the set start point citedabove in the connection identifiers thereof is stored as a setting groupsize.

Subsequently, the flow of the procedure proceeds to the process 168 inwhich change points on the change-point list following the set startpoint are sequentially checked to search for a smallest change point. Asmallest change point is a change point with minimum value following thecurrent change point for which the group size of a logical connectionhaving a connection identifier equivalent to the check point valuethereof which is not greater than the setting group size, or an endpoint of a group of logical connections corresponding to the set startpoint.

The flow of the procedure then continues to a process 169 in which theaffected group size stored in the process 162 is compared with a groupsize set previously. If the affected group size is equal to or smallerthan the previously set group size and the processing is a processing toset up logical connections, the flow of the procedure goes on to aprocess 170 in which a command to set up logical connections from theset start point to the change point is issued to associated connectionswitching exchanges. If the affected group size is greater than thepreviously set group size and the processing is a processing to releaselogical connections, on the other hand, the flow of the procedure goeson to a process 171 in which a command to set up logical connectionsfrom the set start point to the change point is issued to associatedconnection switching exchanges. The flow of the procedure then proceedsto a process 172 to check if the change point is the last change pointon the change-point list. If the change point is the last point, theprocessing is ended.

If the change point is found in the checking process 172 to be not thelast point, on the other hand, the flow of the procedure continues to aprocess 173 in which a logical connection having the connectionidentifier equivalent to the change point value obtained in the process168 thereof is searched for. If such logical connections are found, theflow of the procedure proceeds to a process 174 in which the changepoint is stored as a set start point, and the smallest group size amongthe found logical connections is stored as a setting group size. Theflow of the procedure then returns to the process 168. If a logicalconnection having the connection identifier equivalent to the changevalue point obtained in the process 168 in the connection identifierthereof is not found in the process 173, on the other hand, the flow ofthe procedure continues to a process 175 in which the change point isstored as a set end point. The flow of the procedure then returns to theprocess 166.

The following is a description of an example of an application usingcontrol of logical connections provided by the present invention toone-directional logical connections among terminating nodes, withreference to FIG. 15.

In order to make the diagram simple, FIG. 15 shows a partial state inwhich only some terminating nodes 11 in a communication network areconnected to each other by one-directional logical connections. Morespecifically, the figure is a diagram showing an embodiment implementinga communication network wherein only terminating nodes 11-1 and 11-13are connected to other terminating nodes 11 in the network byone-directional logical connections 3.

As shown in the figure, the embodiment implementing a communicationnetwork comprises twelve terminating nodes 11, that is, terminatingnodes 11-1 to 11-3, 11-5 to 11-10 and 11-13 to 11-15, four edgeconnection switching exchanges 1, that is, connection switchingexchanges 1-1 to 1-4, and two relay connection switching exchanges 1-10and 1-11 which are connected to each other by communication lines 2.One-directional logical connections among the terminating nodes 11 inthis embodiment are set using the initial connection setting specifyinginformation 22 during initialization. The one-directional logicalconnections among the terminating nodes 11 each have a unique connectionidentifier for each destination terminating node 11. In other words,logical connections between source terminating nodes 11 and adestination terminating node 11 have the same connection identifier.Thus, the connection identifiers form so-called multipoint-to-pointconnections. For example, all logical connections toward the terminatingnode 11-1 have a connection identifier of 0x100 and all logicalconnections toward the terminating node 11-2 have a connectionidentifier of 0x101. Now pay attention to the logical connection towardthe terminating node 11-2. A logical connection from the terminatingnode 11-1 to the terminating node 11-2 by way of the connectionswitching exchange 1-1 and a logical connection from the connectionswitching exchange 1-10 to the terminating node 11-2 by way of theconnection switching exchange 1-1 are merged at the connection switchingexchange 1-1 as the connection identifier 0x101. It should be noted thatvalue of a connection identifier is expressed by a string of charactersstarting with the characters 0x to indicate that the rest is a numberexpressed in the hexadecimal format.

In addition, one-directional connections are implemented as groupedlogical connections. FIG. 16 is a diagram showing a typical processingprocedure provided by the present invention to set up a one-directionallogical connection between terminating nodes using logical connectionscontrolled in group units in accordance with the present invention.

As shown in FIG. 16, the procedure begins with a process 181 in whichthe connection switching exchanges 1 and the terminating nodes 11 in thecommunication network are hierarchically classified by a procedure shownin FIG. 17. The flow of the procedure then goes on to a process 182 inwhich a lower level logical connection count variable for each apparatusat each hierarchical level is set to 0. A lower level logical connectioncount variable for each apparatus is used for storing the number oflogical connections from the apparatus to apparatuses at levels lowerthan the apparatus in the hierarchy. Information on spare logicalconnections for each apparatus is made empty to indicate that there isno spare logical connection. In addition, a main upper level apparatusfor each apparatus is selected from apparatuses one level higher thaneach apparatus in the hierarchy considering the importance of theconnection relation between the apparatus and the main upper levelapparatus. Then, the flow of the procedure proceeds to a process 183 inwhich a terminating node 11 at hierarchical level 0 with a lower levellogical connection count of 0 is selected, and the lower level logicalconnection count variable for the apparatus is set to 1.

Subsequently, the flow of the procedure continues to a process 184 tocall recursive processing for grouped one-directional logical connectionassignment shown in FIG. 18, passing the terminating node 11 selected inthe process 183 and a requested-connection count of 1 as parameters. Thecall sets up one-directional logical branch connections using groupedconnections from higher to lower nodes in a tree hierarchy whereconnection switching exchanges 1 are hierarchically connected to theterminating node passed as a parameter.

The flow of the procedure then continues to a process 185 to search foranother terminating node 11 at hierarchical level 0 with a lower levellogical connection count of 0 for which no logical connection has beenset up. If such a terminating node 11 is found, the flow of theprocedure returns to the process 183. If such a terminating node 11 isnot found, on the other hand, the flow of the procedure goes on to alast process 188. In the processing including the process 185 describedso far, all terminating nodes are connected with one-directional groupedlogical connections from higher to lower nodes in the hierarchy. Thus,in the last process 188, by adoption of the conventional routedetermination algorithm, such as the so-called shortest route method,meshed one-directional interterminal connections are set by connectingeach terminating node to the connections, set through the processes181-185, with one-directional logical connections having a greater orequivalent group size.

The hierarchical classification of the process 181 shown in FIG. 16 iscarried out in accordance with a procedure shown in FIG. 17. As shown inFIG. 17, the procedure begins with a process 191 in which a variable nrepresenting a hierarchical level is set to 0, and all the terminatingnodes 11 are classified each as an apparatus at level 0. The flow of theprocedure then goes on to a process 192 at which the variable n isincremented by 1. Then, the flow of the procedure proceeds to a process193 in which connection switching exchanges 1 in the communicationnetwork, that are directly connected to a level-(n−1) terminating node11 or a level-(n−1) connection switching exchange 1 and do not pertainto categories of apparatuses at (n−1) and lower levels, are eachclassified as an apparatus at level n. Subsequently, the flow of theprocedure proceeds to a process 194 to form a judgment as to whether ornot there is still a connection switching exchange 1 in thecommunication network that has not been classified yet. If there isstill a connection switching exchange 1 in the communication networkthat has not been classified yet, the flow of the procedure returns tothe process 192.

The processes 192 to 194 are carried out repeatedly until there is nolonger a connection switching exchange 1 in the communication networkthat has not been classified yet. After the hierarchical classificationis finished, in the communication network shown in FIG. 15, for example,all the terminating nodes 11 are each classified as an apparatus atlevel 0, the edge connection switching exchanges 1-1, 1-2, 1-3 and 1-4directly connected to the terminating nodes 11 are each classified as anapparatus at level 1, and the connection switching exchanges 1-10 and1-11 connected to the edge connection switching exchanges 1-1, 1-2, 1-3and 1-4 are each classified as an apparatus at level 2.

FIG. 18 is a diagram showing a typical processing procedure called inthe process 184 shown in FIG. 16 to set up one-directional logicalconnections using grouped logical connections toward lower hierarchicallevels. As shown in FIG. 18, the procedure begins with a process 201 toform a judgment as to whether or not an upper level apparatus connectedto the apparatus passed as a parameter exists. If a main upper levelapparatus does not exist, the processing is finished. If a main upperlevel apparatus exists, on the other hand, the flow of the proceduregoes on to a process 202 to form a judgment as to whether or not enoughspare logical connections are left in the main upper level apparatus fora request specified by the requested-connection count passed as aparameter. If enough spare logical connections are left, the flow of theprocedure jumps to a process 208. If enough spare logical connectionsare not available, on the other hand, processes 203 to 207 are carriedout to allocate additional spare logical connections.

In the process 203, a number of spare logical connections to be newlyallocated are calculated by adding some extras to the requested numberof connections, and by making the number a multiple of the connectiongroup size for the main upper level apparatus, which is a power of 2.The flow of the procedure goes on to a process 204 to form a judgment asto whether or not another main upper level apparatus further exists at alevel higher than the level of the current main upper level apparatus.If such a main upper level apparatus exists, the flow of the procedureproceeds to a process 205 to recursively call this processing shown inFIG. 18 by passing the main upper level apparatus and the number ofspare logical connections to be added calculated in the process 203 asnew parameters. Connections obtained as a result of the call areregistered as spare logical connections of the main upper levelapparatus. If the outcome of the judgment formed in the process 204indicates that such a main upper level apparatus does not exist, on theother hand, the flow of the procedure proceeds to a process 206 in whichunassigned consecutive connection identifiers are allocated, as many ascalculated in the process 203, and the allocated connection identifiersare registered as those for spare connections of the main upper levelapparatus terminating the spare connections at the main upper levelapparatus. The flow of the procedure then continues to a process 207 inwhich spare logical connections additionally registered in the process205 or 206 are added to the lower level logical connection countvariable of the main upper level apparatus indicating totally allocatedconnections for lower levels.

The processes 202 to 207 assure that as many logical connections asrequired are registered as spare logical connections. Thus, in a process208 following the process 207, the requested number of consecutivelogical connections are finally allocated from the spare logicalconnections of the main upper level apparatus, and a switching table forthe main upper level apparatus specified as a parameter is set so as todistribute and connect the allocated logical connections to theapparatus. The allocated logical connections are returned as a result tothe calling process before finally finishing the processing.

Consider the processing described above by focusing on the connectionswitching exchange 1-1 shown in FIG. 15. The connection switchingexchange 1-1 which is an apparatus at level 1 is connected to the threeterminating nodes 11-1, 11-2 and 11-3, apparatuses at level 0. Thus, inthe process 206, with a connection identifier 0x100 used as a connectionidentifier for the terminating node 11-1, consecutive connectionidentifiers of 0x101 and 0x102 are assigned to the terminating nodes11-2 and 11-3 following the terminating node 11-1. In addition, sincethe group size is set to four in the present embodiment, grouped logicalconnections having connection identifiers 0x100 to 0x103 are set fromthe connection switching exchange 1-10 toward the connection switchingexchange 1-1 in the process 206. In particular, connection identifiers0x100 to 0x102 are distributed and connected to the terminating nodes11-1 to 11-3, respectively.

In addition, in the connection switching exchange 1-10, logicalconnections with connection identifiers 0x104 to 0x107 toward theconnection switching exchange 1-2 are gathered with logical connectionswith connection identifiers 0x108 to 0x10b toward the connectionswitching exchange 1-3. Furthermore, in the process 188, the terminatingnode 11-13 is connected to the connection switching exchange 1-2 in thisembodiment by a group of logical connections having a greater group sizeof eight using connection identifiers 0x100 to 0x107.

That is to say, the embodiment described above is characterized by thefollowing. For i>=1, one-directional interterminal logical connectionsfrom an apparatus at a hierarchical level i to apparatuses at ahierarchical level i-1 have consecutive connection identifiers. Inaddition, in an apparatus at level i, a proper number of connectionidentifiers are reserved for future expansion of connection ofapparatuses. The total number of connection identifiers assigned toone-directional interterminal logical connections from an apparatus atlevel i to apparatuses at level i−1 including the reserved ones is madeequal to a multiple of a group unit, and the connection identifiers forthe logical connections are assigned in the group unit. A group oflogical connections having the connection identifiers assigned theretoare set in the group unit from all apparatuses at level i+1 directlyconnected to an apparatus at level i to the apparatus at level i. At aconnection switching exchange at level i, a group of logical connectionsfrom apparatuses at level (i+1) to an apparatus at level i aredistributed to be connected to logical connections or a group of logicalconnections from the apparatus at level i to apparatuses at level i−1.In addition, in order to setup meshed interterminal connections,one-directional logical connections are connected from each terminatingnode to the logical connections, which are set in group units from highto low hierarchical layers as described above, in a connection-groupunit equal to or greater than that for the connections from high to lowlayers.

The embodiment shown in FIG. 15 adopts a method whereby, in the process188, for logical connections from each terminating node 11, a group unitof eight is used and, in each connection switching exchange 1, there isno overlap of connection-switching information on logical connectionsamong group units. In the grouping technique described above, wherebyconnection-switching information on a group of logical connections witha small group unit takes precedence of connection-switching informationon a group of logical connections with a large group unit, however, itis possible to adopt a method in which pieces of connection-switchinginformation overlap each other among grouped logical connections in aconnection switching exchanges 1.

FIG. 19 is a diagram showing another partial configuration ofone-directional logical connections between terminating nodes usinglogical connections controlled in group units wherein, in the process188, by using a group size of sixteen, one-directional logicalconnections from higher to lower level apparatuses are connected fromeach terminating node 11 using logical connections in the group unit ofsixteen. In this embodiment, for example, at the connection switchingexchange 1-1, logical connections in the group unit of sixteen havingconnection identifiers 0x100 to 0x10f are switched from the terminatingnode 11-1 to the terminating node 11-10 through the connection switchingexchange 1-1. On the other hand, logical connections switched from theterminating node 11-1 to the terminating nodes 11-1, 11-2 and 11-3 alsothrough the connection switching exchange 1-1 are set up by usinglogical connections with connection identifiers 0x100, 0x101 and 0x102respectively each having a group size of 1. Thus, the connectionidentifiers 0x100, 0x101 and 0x102 overlap with those in the differentgroup units. In this case, the connection identifiers 0x100, 0x101 and0x102 in the latter group unit take precedence, causing theswitching-unit information in the former group unit with a value ofsixteen to be ignored.

The embodiment described above shows a typical implementation ofone-directional logical connections among the terminating nodes 11. Itshould be noted, however, that the embodiment can also be applied to acase wherein the level of each apparatus is virtually lowered by 1 layerwith apparatuses at level 1 each considered to be a terminating node,and one-directional meshed logical connections are set up among edgeconnection switching exchanges.

Next, control of routes traveled by IP data using one-directionallogical connections among terminating nodes 11 will be explained withreference to FIGS. 20, 21 and 22.

In the first place, the network management unit 13 is provided withIP-route information 26 showing which terminating node or nodes 11 areindicated by a destination IP address or a group of destination IPaddresses included in IP data, that is, which terminating node or nodes11 the IP data with a destination IP address or a group of destinationIP addresses should be transmitted to, or which terminating node ornodes 11 IP data should be transmitted through. During initialization,the grouped-connection management means 18 employed in the networkmanagement unit 13 carries out processing in accordance with a procedureshown in FIG. 21 by using the IP-route information 26.

As shown in FIG. 21, the procedure for initialization begins with aprocess 211 in which the grouped-connection management means 18 employedin the network management unit 13 creates IP/connection transformationinformation 27 by using the IP-route information 26 and theconnection-control information 30. The IP/connection transformationinformation 27 is used for transforming an IP address or a group of IPaddresses into connection identifiers of one-directional interterminallogical connections toward destination terminating nodes 11 which wereset up among terminating nodes 11 during the initialization.

The flow of the procedure then goes on to a process 212 in which thegrouped-connection management means 18 employed in the networkmanagement unit 13 transmits the IP/connection transformationinformation 27 to edge connection switching exchanges 1 directlyconnected to the terminating nodes 11 through the operation-controlcommunication lines 15. Each of the edge connection switching exchanges1 is provided with an IP/connection transformation mechanism 71 as partof the control mechanism 9. In a process 213 following the process 212,the IP/connection transformation mechanism 71 receives the IP/connectiontransformation information 27 and stores the information 27 in the edgeconnection switching exchange 1 by way of a signal line 58.

FIG. 22 is a diagram showing a typical transmission procedure forcontrolling a route of an IP data packet through a one-directionallogical connection between terminating nodes 11 using a logicalconnection after the initialization shown in FIG. 21. As shown in FIG.22, the procedure begins with a process 221 in which the terminatingnodes 11 transmit IP data to the edge connection switching exchange 1 byusing the IP logical connections 72. The IP/connection transformationmechanism 71 is connected to terminating nodes 1 to which the edgeconnection switching exchange 1 is linked directly by using IP logicalconnections 72 having predefined connection identifiers for IPprocessing. The flow of the procedure then goes on to a process 222 inwhich, upon receiving IP data from a terminating node 11, theIP/connection transformation mechanism 71 uses a destination IP addressrecorded in the IP header of the IP data received from a terminatingnode 11 as a key to search the IP/connection-information 27 stored inthe edge connection switching exchange 1 for a connection identifier ofa one-directional interterminal logical connection 80 toward adestination terminating node 11.

Then, the flow of the procedure proceeds to a process 223 in which theIP/connection transformation mechanism 71 replaces connection-identifierinformation 62 in each data packet 60 of the IP data with the identifiervalue of the one-directional interterminal logical connection 80obtained in the process 222. Subsequently, the flow of the procedurecontinues to a process 224 in which the IP/connection transformationmechanism 71 searches the switching table 4 through the signal line 58for information on an output transmission line corresponding to theidentifier value of the one-directional interterminal logical connection80.

The flow of the procedure then goes on to a process 225 in which theIP/connection transformation mechanism 71 outputs each data packet 60 ofthe IP data with the connection-identifier information 62 thereofreplaced by the identifier value of the one-directional interterminallogical connection 80 along with the information on the outputcommunication line to the switch mechanism 6 by way of a communicationline 56-0. Then, the flow of the procedure proceeds to a process 226 inwhich the switch mechanism 6 carries out connection switching based onthe information on the output communication line supplied thereto forthe data packets 60 of the IP data, whereby the packets 60 aretransmitted to a communication line 2 specified by the information onthe output communication line. Finally, the flow of the procedurecontinues to a process 227 in which each of the connection switchingexchanges 1 carries out connection switching to a one-directionalinterterminal logical connection 80 to a destination terminating node 11in accordance with the identifier of the logical connection 80, wherebythe data packets 60 are transmitted to the destination.

In the embodiment described above, the IP/connection transformationmechanism 71 employed in each of the edge connection switching exchanges1 directly transfers IP data. It should be noted that it is alsopossible to provide another embodiment in which the IP/connectiontransformation mechanism 71 supplies only IP/connection transformationinformation 27 for transforming an IP address into an identifier of aone-directional interterminal logical connection. In this case, first ofall, a terminating node 11 obtains the IP/connection transformationinformation 27 from the IP/connection transformation mechanism 71. Then,after transforming a destination IP address of IP data to be transmittedinto an identifier of a desired one-directional interterminal logicalconnection, the terminating node 11 transmits the IP data to thedestination by using the identifier of the one-directional interterminallogical connection. FIG. 23 is a diagram showing a typical configurationof a communication network for this embodiment provided by the presentinvention to transmit an IP data packet through one-directional logicalconnections between terminating nodes using logical connectionscontrolled in group units, and FIG. 24 is a diagram showing a typicaltransmission procedure adopted by the communication network shown inFIG. 23.

As shown in FIG. 23, each of the terminating nodes 11 is provided withan IP/connection transformation cache 28 for storing some of theIP/connection transformation information 27 used for transforming adestination IP address of IP data transmitted in the past. As for theprocedure shown in FIG. 24, the flow begins with a process 231 in whichthe terminating node 11 searches the IP/connection transformation cache28 prior to transmission of IP data in order to form a judgment as towhether or not an entry corresponding to a destination IP addressincluded in the IP data exists in the cache 28.

If such an entry does not exist in the IP/connection transformationcache 28, the flow of the procedure goes on to a process 232 in whichthe terminating node 11 transmits information on the destination IPaddress to the IP/connection transformation mechanism 71 employed in theedge connection switching exchange 1 directly connected to theterminating node 11 by using the IP logical connection 72 in order toobtain IP/connection transformation information 27. Then, the flow ofthe procedure proceeds to a process 233 in which, upon receiving theinformation on the destination IP address, the IP/connectiontransformation mechanism 71 searches the IP/connection transformationinformation 27 stored in the edge connection switching exchange 1 for adesired portion associated with the destination IP address, andtransmits the desired portion of the IP/connection transformationinformation 27 to the terminating node 11, which requested theinformation, as a result of the search operation.

Subsequently, the flow of the procedure continues to a process 234 inwhich the terminating node 11 stores the desired portion of theIP/connection transformation information 27 transmitted by theIP/connection transformation mechanism 71 in response to the destinationIP address in the IP/connection transformation cache 28. Upon completionof the processes 232, 233 and 234, desired IP/connection transformationinformation 27 is cataloged in the IP/connection transformation cache28.

The flow of the procedure then goes on to a process 235 in which theterminating node 11 finds out an identifier of a one-directionalinterterminal logical connection 80 corresponding to the destination IPaddress from the cataloged IP/connection transformation information 27and then transmits the IP data to the edge connection switching exchange1 by using the identifier of the one-directional interterminal logicalconnection 80. Then, the flow of the procedure continues to a process236 in which each of the connection switching exchanges 1 carries outconnection switching of the one-directional interterminal logicalconnection 80 to a destination terminating node 11 in accordance withthe identifier of the logical connection 80, and transmits data packets60 of the IP data to the destination.

In the embodiments shown in FIGS. 23 and 24, only part of theIP/connection transformation information 27 is stored in theIP/connection transformation cache 28. It should be noted, however, thata terminating node 11 may serve as a gateway connected to an externalnetwork. In this case, the IP/connection transformation cache 28 is usedfor storing the entire IP/connection transformation information 27.Thus, in place of the processes 232 to 234 shown in FIG. 24, in whichonly a desired portion of the IP/connection transformation information27 is acquired dynamically, the terminating node 11 makes a request toan edge connection switching exchange 1 connected directly to theterminating node 11 to transmit the entire IP/connection transformationinformation 27 during initialization of the terminating node 11 so thatit is stored in the IP/connection transformation cache 28 thereof inadvance. As an alternative, in the process 213 of the initializationshown in FIG. 21 which is common to the immediately precedingembodiment, after the IP/connection transformation mechanism 71 employedin the edge connection switching exchange 1 receives the IP/connectiontransformation information 27 from the grouped-connection managementmeans 18 employed in the network management unit 18, the edge connectionswitching exchange 1 passes on the entire IP/connection transformationinformation 27 to a terminating node 11 which requires the information27 and is directly connected to the exchange 1, by way of an IP logicalconnection. The terminating node 11 stores the entire IP/connectiontransformation information 27 received from the grouped-connectionmanagement means 18 employed in the network management unit 13 in theIP/connection transformation cache 28 of the terminating node 11. Inparticular, in the case of the latter scheme, wherein terminating nodes11 directly connected to an edge connection switching exchange 1 eachhave the entire IP/connection transformation information 27 receivedfrom the network management unit 13 stored in the IP/connectiontransformation cache 28 of the terminating node 11, it is necessary forthe edge connection switching exchange 1 to merely pass on theIP/connection transformation information 27 to the terminating nodes 11without the need to store the information 27.

According to a still another embodiment, there is provided a methodwhereby a terminating node 11 transmits IP data to a source edgeconnection switching exchange 1, the edge connection switching exchange1 then passes on the IP data to a destination edge connection switchingexchange 1 by using a one-directional logical connection between thesource edge connection switching exchange 1 and the destination edgeconnection switching exchange 1, and the destination edge connectionswitching exchange 1 finally delivers the IP data to a destinationterminating node 11. An example of an embodiment and a procedure adoptedby the embodiment for controlling the route of IP data are shown inFIGS. 25, 26 and 27. To be more specific, FIG. 25 is a diagram showingthe configuration, FIG. 26 is a diagram showing a typical procedure forinitialization and FIG. 27 is a diagram showing a typical transmissionprocedure.

As shown in FIG. 25, the network management unit 13 is provided withIP-route information 26 showing which terminating node or nodes 11 theIP data with an IP address, or a group of IP addresses, respectively,should be transmitted to and which edge connection-switching exchange orswitching exchanges 1 IP data should be transmitted through, or whichterminating node or nodes 11 and which edge connection-switchingexchange or switching exchanges 1 IP data should be transmitted through.

During initialization, the grouped-connection management means 18employed in the network management unit 13 carries out processing inaccordance with a procedure shown in FIG. 26 by using the IP-routeinformation 26. As shown in FIG. 26, the procedure for initializationbegins with a process 241 in which the grouped-connection managementmeans 18 employed in the network management unit 13 createsIP/inter-edge-exchange-connection transformation information 73 by usingthe IP-route information 26 and the connection-control information 30.The IP/inter-edge-exchange-connection transformation information 73 isused for transforming an IP address or a group of IP addresses intoconnection identifiers of one-directional inter-edge-exchange logicalconnections toward destination edge connection switching exchanges 1between edge connection switching exchanges 11 which were set up amongterminating nodes 11 during the initialization.

Then, the flow of the procedure proceeds to a process 242 in which thegrouped-connection management means 18 employed in the networkmanagement unit 13 creates IP/terminal-line transformation information74 used for transforming information on a destination edge connectionswitching exchange included in IP data into information indicating whichterminating node and which communication line the IP data should betransmitted to and transmitted through by using the IP/route information26 and the connection-configuration information 21 for an IP address ora group of IP addresses.

The flow of the procedure then goes on to a process 243 in which thegrouped-connection management means 18 employed in the networkmanagement unit 13 transmits the IP/inter-edge-exchange-connectiontransformation information 73 and the IP/terminal-line transformationinformation 74 to edge connection switching exchanges 1 directlyconnected to the terminating nodes 11 through the operation-controlcommunication lines 15. Each of the edge connection switching exchanges1 is provided with an IP/connection transformation mechanism 71 and anIP/terminal-line transformation mechanism 75 as part of the controlmechanism 9.

In a process 244 following the process 243, the IP/connectiontransformation mechanism 71 receives theIP/inter-edge-exchange-connection transformation information 73 and theIP/terminal-line transformation information 74 and stores theinformation in the edge connection switching exchange 1 by way of asignal line 58.

FIG. 27 is a diagram showing a typical transmission procedure forcontrolling routes of an IP data packet through one-directional logicalconnections between terminating nodes 11 using logical connections afterthe initialization shown in FIG. 26.

The IP/connection transformation mechanism 71 employed in an edgeconnection switching exchange 1 is connected to a source terminatingnode 11 directly connected to the edge connection switching exchange 1by an IP transmission logical connection 78. On the other hand, theIP/terminal-line transformation mechanism 75 employed in an edgeconnection switching exchange 1 is connected to a destinationterminating node 11 directly connected to the edge connection switchingexchange 1 by an IP reception logical connection 79. Aninter-edge-exchange one-directional logical connection 81 toward adestination edge connection switching exchange 1 set up during theinitialization shown in FIG. 26 is connected to the IP/terminal-linetransformation mechanism 75 employed in the edge connection switchingexchange 1 also during the initialization.

As shown in FIG. 27, the procedure begins with a process 251 in which aterminating node 11 transmits IP data to a source edge connectionswitching exchange 1 by using the IP transmission logical connection 78.The flow of the procedure then goes on to a process 252 in which, uponreceiving the IP data from the terminating node 11, the IP/connectiontransformation mechanism 71 uses a destination IP address recorded inthe IP header of the IP data received from the terminating node 11 as akey to search the IP/inter-edge-exchange-connection transformationinformation 73 stored in the edge connection switching exchange 1 for aconnection identifier of a one-directional inter-edge-exchange logicalconnection 81 toward a destination edge connection switching exchange 1.Then, the flow of the procedure proceeds to a process 253 in which theIP/connection transformation mechanism 71 replaces connection-identifierinformation 62 in each data packet 60 of the IP data with the identifiervalue of the one-directional inter-edge-exchange logical connection 81obtained in the process 252.

Subsequently, the flow of the procedure continues to a process 254 inwhich the IP/connection transformation mechanism 71 searches theswitching table 4 through the signal line 58 for information on anoutput transmission line corresponding to the identifier value of theone-directional inter-edge-exchange logical connection 81. The flow ofthe procedure then goes on to a process 255 in which the IP/connectiontransformation mechanism 71 outputs each data packet 60 of the IP datawith the connection-identifier information 62 thereof replaced by theidentifier value of the one-directional inter-edge-exchange logicalconnection 81 along with the information on the output communicationline to the switch mechanism 6 by way of a communication line 56-0.

Then, the flow of the procedure proceeds to a process 256 in which theswitch mechanism 6 carries out connection switching based on theinformation on the output communication line supplied thereto for thedata packets 60 of the IP data, transmitting the packets 60 to thecommunication line 2 specified by the information on the outputcommunication line. Subsequently, the flow of the procedure continues toa process 257 in which each of the connection switching exchanges 1carries out connection switching to the one-directionalinter-edge-exchange logical connection 81 to a destination edgeconnection switching exchange 1 in accordance with the identifier of thelogical connection 81, transmitting the data packets 60 to thedestination.

The flow of the procedure then goes on to a process 258 in which theIP/terminal-line transformation mechanism 75 employed in the destinationedge connection switching exchange 1 receives the IP data transmitted bythe source edge connection switching exchange 1 through theone-directional inter-edge-exchange logical connection 81 and-obtainsinformation on a communication line to the destination terminating node11 which is supposed to receive the IP data by referring to theIP/terminal-line transformation information 74.

Then, the flow of the procedure proceeds to a process 259 in which theIP/terminal-line transformation mechanism 75 replaces the information 62on a connection identifier recorded in each data packet 60 of the IPdata with the value of the identifier of the IP/reception logicalconnection 79. Subsequently, the flow of the procedure continues to aprocess 260 in which the IP/terminal-line transformation mechanism 75delivers each data packet 60 of the IP data with the information 62 on aconnection identifier thereof replaced by the value of the identifier ofthe IP/reception logical connection 79 along with the information on thecommunication line to the destination terminating node 11 obtained inthe process 258 to the switch mechanism 6 through a signal line 56.Finally, the flow of the procedure proceeds to a process 261 in whichthe switch mechanism 6 carries out connection switching based on theinformation on the output communication line supplied thereto for thedata packets 60 of the IP data, and transmits the packets 60 to thedestination terminating node 11 by way of the communication linespecified by the information on the output communication line.

In the embodiments described above, logical connections set up duringinitialization are used as grouped logical connections. The following isa description of embodiments utilizing grouped logical connections inresponse to a request to set up or release a logical connection which ismade by any terminating node 11 dynamically.

As explained in the description of the conventional connection switchingexchange with reference to FIG. 2, a request to set up or release alogical connection which is made by any terminating node 11 dynamicallyis transmitted to the connection setup/release mechanism 10 employed inthe edge connection switching exchange 1 through the signaling logicalconnection 82 to be processed by the connection setup/release mechanism10. In the connection setup/release mechanism 10 implemented by anembodiment of the present invention, however, unlike the conventionalconnection switching exchange, a logical connection from a requestingterminating node 11 to a destination is not actually set up or releasedfor each request to set up or release the logical connection made by theterminating node 11. Instead, in the edge connection switching exchange1, a means is provided to serve as a buffer for requests to set up orrelease the logical connections made by a terminating node 11, and agroup of logical connections from the edge connection switching exchange1 to destination terminating nodes 11 are set up or released in a newconnection setting unit equal to a multiple of a group unit. That is tosay, the logical connections in the new connection setting unit aredivided into small numbers of logical connections, and a request made bya terminating node 11 to set up or release logical connections isprocessed by picking up a small number of logical connections from thebuffer, and by setting or releasing a portion of the connections thatare between the terminating node 11 and the logical connections pickedup. For this reason, the connection setup/release mechanism 10 employedin the edge connection switching exchange 1 provided by the presentinvention has terminal-connection-control information 63 for controllingthe status of assignment to terminating nodes 11 for each group oflogical connections set in the new connection setting unit size forbuffering purposes.

The terminal-connection-control information 63 includes time-outinformation 70 for providing a timing to release a new setting unit oflogical connections. A typical format of the terminal-connection-controlinformation 63 is shown in FIG. 28. As shown in the figure, for eachgroup of logical connections set in the new setting unit, in addition tothe time-out information 70, the terminal-connection-control information63 comprises information on destinations 64 for the connections,information on attributes 65 for the connections, a head connectionidentifier value 66 for the connections, the number of set logicalconnections 67, the number of free logical connections 68, that is, thenumber of logical connections unassigned to terminating nodes 11, andinformation on free connection identifiers 69.

FIG. 29 shows a typical procedure for implementing a processing toprocess a request to set up a logical connection made by a terminatingnode 11 by using terminal-connection-control information 63. As shown inthe figure, the procedure begins with a process 271 in which theterminating node 11 issues a request to set up a new logical connectionto an edge connection switching exchange 1 through a signaling logicalconnection 82.

The flow of the procedure then goes on to a process 272 in which theconnection setup/release mechanism 10 of the edge connection switchingexchange 1 receiving the request checks pieces ofterminal-connection-control information 63 corresponding to thedestination and attributes specified in the request to search forterminal-connection-control information 63 with a non-zero number offree logical connections 68. If terminal-connection-control information63 with a non-zero number of free logical connections 68 is found, theflow of the procedure jumps to a process 275. If the number of freelogical connections 68 of each terminal-connection-control information63 corresponding to the destination and attributes specified in therequest is 0, on the other hand, the flow of the procedure proceeds to aprocess 273 in which the connection setup/release mechanism 10 of theedge connection switching exchange 1 resorts to the grouped-connectionmanagement means 18 employed in the network management unit 13 throughan operation-control communication line 15 to set up a group of logicalconnections with a group size equal to the new connection setting unitdescribed above, that is, to set up a group of logical connectionshaving the destination and the attributes specified in the request witha group size equal to the new connection setting unit.

Then, the flow of the procedure proceeds to a process 274 in which theconnection setup/release mechanism 10 creates newterminal-connection-control information 63 for the new group of logicalconnections obtained as a result of the process 273, puts all thelogical connections in the group in an unassigned state, initializes alldata except the time-out information 70 and catalogs the newterminal-connection-control information 63.

Subsequently, the flow of the procedure continues to the process 275 inwhich the connection setup/release mechanism 10 fetches as manyunassigned connection identifiers as requested by referring to theinformation on free connection identifiers 69 of theterminal-connection-control information 63 for unassigned logicalconnections meeting the request, logical connections found in theprocess 272 or cataloged in the process 274, subtracts the number offetched connection identifiers from the number of free connectionidentifiers 68, puts the fetched connection identifiers in an assignedstate and updates the information on free connection identifiers 69.

The flow of the procedure then goes on to a process 276 in which theswitching table 4 is set up to extend and link the fetched connectionsto the terminating node 11 with the connection identifiers obtained inthe process 275. Finally, the flow of the procedure continues to aprocess 277 in which the connection setup/release mechanism 10 transmitsthe connection identifier obtained in the process 275 to the terminatingnode 11 making the request.

FIG. 30 is a typical procedure of an embodiment implementing processingto process a request to release a logical connection made by aterminating node 11. As shown in the figure, the procedure begins with aprocess 281 in which the terminating node 11 issues a request to releasea logical connection to an edge connection switching exchange 1 througha signaling logical connection 82. The flow of the procedure then goeson to a process 282 in which the connection setup/release mechanism 10of the edge connection switching exchange 1 receiving the requestsearches for terminal-connection-control information 63 for the logicalconnection to be released on the basis of information on a connectionidentifier.

Then, the flow of the procedure proceeds to a process 283 in which theconnection setup/release mechanism 10 increases the number of freelogical connections 68 of the terminal-connection-control information 63found in the process 282 by the number of logical connections beingreleased and updates the information on free connection identifiers 69to change the status of assignments of logical connections beingreleased to an unassigned one. Subsequently, the flow of the procedurecontinues to a process 284 in which the connection setup/releasemechanism 10 invalidates an entry in the switching table 4 correspondingto the logical connection being released.

The flow of the procedure then goes on to a process 285 in which theconnection setup/release mechanism 10 sets the current time in thetime-out information 70 of the terminal-connection-control information63 in case the number of free logical connections 68 becomes equal tothe number of set logical connections 67 of theterminal-connection-control information 63, that is, in case all setlogical connections become free or have an unassigned status. Thetime-out information 70 is checked by the time-out processing ofunassigned logical connections of FIG. 31, which is invokedperiodically. If the status of terminal-connection-control information63 in which the number of free logical connections 68 thereof is equalto the number of set logical connections 67 continues for more than apredetermined period of time, the grouped-connection management means 18employed in the network control means 13 is requested to release a groupof unassigned logical connections associated with theterminal-connection-control information 63. Finally, the flow of theprocedure proceeds to a process 286 in which the result of theprocessing to release a logical connection is transmitted to theterminating node 11 making the request for the processing.

FIG. 31 is a diagram showing a typical procedure for the aforementionedprocessing to release a group of logical connections set up in newconnection setting units, which is carried out periodically by the edgeconnection switching exchange as a part of the processing to process arequest to release a logical connection made by a terminating node. Asshown in the figure, the procedure begins with a process 287 in whichpieces of terminal-connection-control information 63, with the number offree logical connections 68 thereof equal to the number of set logicalconnections 67, are sequentially fetched one piece after another. Ifsuch terminal-connection-control information 63 does not exist, theperiodically invoked processing is finished. If suchterminal-connection-control information 63 exists, on the other hand,the flow of the procedure goes on to a process 288 to check the time-outinformation 70 of the terminal-connection-control information 63 to becompared with the current time. If the result of the comparisonindicates that a predetermined period of time has not elapsed yet, theflow of the procedure returns to the process 287. If the predeterminedperiod of time has elapsed, on the other hand, the flow of the procedureproceeds to a process 289 in which the grouped-connection managementmeans 18 employed in the network management unit 13 is requested torelease a group of all logical connections associated with theterminal-connection-control information 63 with a group size equal tothe new connection setting unit described above and to delete theterminal-connection-control information 63. The flow of the procedurethen returns to the process 287.

Next, an embodiment implementing failure handling by using groupedlogical connection control provided by the present invention will beexplained. Basically, there are two techniques to handle a failure byusing the grouped logical connection control. According to one of thetechniques, a plurality of group sizes are used and a group of logicalconnections for a detour path with overlapping connection identifiersare set up in advance. This technique to handle a failure is thusapplicable to a case in which a failing member is a group of logicalconnections already having a detour path. FIG. 32 is a diagram showingan embodiment implementing this technique to handle a failure of one ofthe one-directional interterminal logical connections shown in FIG. 19.

More specifically, FIG. 32 shows a case in which a failure occurs on acommunication line 2 from the connection switching exchange 1-11 to theconnection switching exchange 1-3. In this example, the failure affectsa group of logical connections from the connection switching exchange1-11 to the connection switching exchange 1-3 having connectionidentifiers 0x108 to 0x10b. In this example, however, another group oflogical connections having connection identifiers 0x100 to 0x10foverlapping the connection identifiers 0x108 to 0x10b of the group oflogical connections affected by the failure have already been set up. Inthis other group of logical connections, a subgroup of logicalconnections having connection identifiers 0x108 to 0x10b are connectedto the connection switching exchange 1-3 through the connectionswitching exchange 1-10. Thus, by using this subgroup of logicalconnections, a detour path for the failing member can be made. That isto say, by merely invalidating the setting of the group of logicalconnections from the connection switching exchange 1-11 to theconnection switching exchange 1-3 affected by the failure in theswitching table 4 of the connection switching exchange 1-11, the problemcaused by the failure can be solved.

The other technique to handle a failure by using grouped logicalconnections is applicable to a case in which no logical connections areset up in advance for a detour path like the one described above. FIG.33 is a diagram showing an embodiment implementing this technique tohandle a failure of one of the one-directional interterminal logicalconnections shown in FIG. 15. More specifically, FIG. 33 shows a case inwhich a failure occurs on a communication line 2 from the connectionswitching exchange 1-11 to the connection switching exchange 1-3. Unlikethe case shown in FIG. 32, however, in the example shown in FIG. 33, thefailure affects a group of logical connections from the connectionswitching exchange 1-11 to the connection switching exchange 1-3 havingconnection identifiers 0x108 to 0x10b for which no detour logicalconnections have been set up in advance.

In order to handle this failure, a group of detour logical connections83 from the connection switching exchange 1-11 to the connectionswitching exchange 1-3 through the connection switching exchange 1-10are set up in a group unit of the group of logical connections affectedby the failure. In this case, the connection identifiers of the group oflogical connections affected by the failure are used as they are asidentifiers assigned to a group of logical connections typically set upfrom the connection switching exchange 1-11 to the connection switchingexchange 1-10 to be linked to a group of logical connections already setup between the connection switching exchange 1-10 and the connectionswitching exchange 1-3. In case logical connections can not be shareddue to a problem, such as a shortage of the bandwidth or the like,however, another group of logical connections with connectionidentifiers 0x208 to 0x20b can be allocated to replace the group oflogical connections affected by the failure. In this case, connectionswitching is carried out in the connection switching exchange 1-11 andthe connection switching exchange 1-3 to link the other group of logicalconnections with connection identifiers 0x208 to 0x20b to the group oflogical connections with connection identifiers 0x108 to 0x10b.

The procedure for implementing the two techniques to handle a failure asdescribed above will be explained once more by referring to FIG. 34. Asshown in the figure, the procedure begins with a process 291 in which,upon detecting a failure by using some methods, the grouped-connectionmanagement means 18 employed in the network management unit 13identifies a failing group of logical connections and a failing routeaffected by the failure by referring to the connection-controlinformation 30 and the connection-configuration information 21.

The flow of the procedure then goes on to a process 292 to examinewhether or not a group of detour logical connections for the failinggroup of logical connections with a group size greater than the groupsize of the failing group of logical connections have already been setup by referring to the connection-control information 30. If a group ofdetour logical connections have already been set up, the flow of theprocedure proceeds to a process 293 in which the grouped-connectionmanagement means 18 gives a command to connection switching exchanges 1on the failing route through operation-control communication lines 15 toinvalidate connection switching for the failing group of logicalconnections. Then, the flow of the procedure proceeds to a process 294in which the grouped-connection management means 18 updates theconnection-control information to reflect the invalidation and finishesthe processing. If the result of the examination in the process 292indicates that a group of detour logical connections have not been setup, on the other hand, the flow of the procedure continues to processingstarting with a process 295 in which, in order to minimize the impact ofthe failure on other members, a detour route is set in accordance withthe following procedure as a transient part of the processing to handlethe failure.

First of all, in the process 295, a detour route is determined byreferring to the connection-control information 30 and theconnection-configuration information 21. Then, the flow of the proceduregoes on to a process 296 to form a judgment based on consideration ofconditions, such as the bandwidth, as to whether the connectionidentifiers of the failing group of logical connections are to be usedas they are as connection identifiers of a group of detour logicalconnections or other connection identifiers are to be assigned to thegroup of detour logical connections. If necessary, new connectionidentifiers are thus assigned to the group of detour logicalconnections.

The flow of the procedure then proceeds to a process 297 in which acommand is given to connection switching exchanges 1 at locations on thedetour route determined in the process 295 by way of operation-controlcommunication lines 15 to carry out connection switching on the group oflogical connections having detour connection identifiers with a groupsize equal to that of the failing group of logical connections.

After the processing to switch a group of detour logical connections forthe connection switching exchanges 1 at locations on the detour route iscompleted, the flow of the procedure then continues to a process 298 inwhich a command is given to a connection switching exchange 1 or 6terminating node 11 at the end on the source side of the detour route tocarry out connection switching to link a group of a logical connectionsconnected to the failing group of logical connections to the group ofdetour logical connections switched in the process 297 and having agroup size equal to that of the failing group of logical connections. Itshould be noted that, in the case of a failing group of logicalconnections composed of bi-directional logical connections, one of theends of the detour route may be regarded as a source.

After the processing to switch the logical connections in a connectionswitching exchange 1 or a terminating node 11 at the end on the sourceside of the detour route is completed, the flow of the procedure thencontinues to a process 299 in which a command is given to a connectionswitching exchange 1 or a terminating node 11 at the end on thedestination side of the detour route to carry out connection switchingto link a group of logical connections connected to the failing group oflogical connections to the group of detour logical connections switchedin the process 297 and having a group size equal to that of the failinggroup of logical connections. Finally, the flow of the procedure goes onto a process 300 in which the connection-control information 30 isupdated to reflect the setting of the detour route.

In the embodiment shown in FIG. 1, the network management unit 13 isconnected to connection switching exchanges 1 by operation-controlcommunication lines 15 implemented on an operation-control network 14.In the case of an embodiment shown in FIG. 35, on the other hand, thenetwork management unit 13 is connected by communication lines 2directly to the communication network, which includes connectionswitching exchanges 1 serving as relay apparatuses. In this case, anoperation-control logical connection 84 having a connection identifierdetermined in advance for use as an operation-control communication lineserves as a logical connection for an operation-control communicationline 15 of the embodiment shown in FIG. 1.

The grouped-connection management means 18 employed in the networkmanagement unit 13 can be connected to a variety of mechanisms employedin the control mechanism 9 of a connection switching exchange 1, such asthe connection setup/release mechanism 10, by the operation-controllogical connection 84. It should be noted that, in the embodiment shownin FIG. 35, a unique connection identifier is used for each connectionswitching exchange 1 and an operation control logical connection 84 isset up individually for each connection switching exchange 1.

In addition, in the embodiments described so far, one control mechanism9 is provided for each connection switching exchange 1. In the case ofan embodiment shown in FIG. 36, on the other hand, a control mechanism 9is provided for each communication line 2. In addition, a logicalconnection distribution mechanism 85 for controlling distribution oflogical connections to submechanisms in a control mechanism 9 isprovided for each control mechanism 9 to handle only data packets 60 ofthe logical connections for the control mechanism 9. In addition, avariety of mechanisms in the control mechanism 9 of the embodiment caneach be provided for a communication line 2.

In the embodiments described above, only one network management unit 13is provided for the entire communication network. It should be notedthat, if unitary control of all logical connections in the entirecommunication network in group units can be implemented, typically, aplurality of network management units are provided. In this case, byadopting a system like a distributed data base, a cache is provided ineach of the control management units for implementing control ofconsistency of connection-control information. Processing is distributedamong the same plurality of network management units according to rangesof distribution of connection identifiers and ranges of distribution ofconnection switching exchanges.

According to the present invention, even in a large-scale communicationnetwork, there will be no cases in which connection identifiers andswitching-table entries are not sufficient, allowing switching ofhigh-speed IP packets to be implemented. In actuality, in the switchingof an IP packet, a logical connection already set up between terminatingnodes is used. Thus, high speed switching operations can be sustainedwithout the need to set up a logical connection at the switching of anIP packet. In addition, logical connections between terminating nodesare set up by adopting a system whereby logical connections controlledin group units over the entire communication network are used forintegrating, distributing and linking groups of hierarchical logicalconnections. As a result, even if logical connections are set betweenterminating nodes, only connection identifiers about equal in number toterminating nodes are required. In addition, by using the connectionswitching exchange provided by the present embodiment, only extremelyfew switching-table entries are needed to allow switching at high speedto be implemented by hardware.

Furthermore, even in a case where logical connections need to be set updynamically during communication of data requiring assurance ofbandwidth, such as communication of audio and video data, according tothe present invention, logical connections are set up and released ingroup units provided by the present invention in a connection switchingexchange, instead of setting up or releasing a logical connection from asource terminating node to a destination node each time a request to setup or release a logical connection is received individually from thesource terminating node. Thus, by adopting a technique of setting-up orreleasing logical connections in a batch operation, there can beexhibited effects that the number of actual operations to set up orrelease logical connections can be reduced and that the number ofswitching-table entries can be decreased.

In addition, according to the present invention, even in the case of alarge-scale network, unitary control of logical connections can beexecuted, allowing a failure to be recovered with ease. In theconventional connection switching exchange, switching is carried out byusing connection identifiers individually controlled by and stored inthe connection switching exchange. According to the present invention,on the other hand, logical connections controlled in a unitary mannerover the entire communication network are used for carrying outswitching of logical connections in each connection switching exchange.Thus, even when information on connection switching is lost in aconnection switching exchange in the event of a failure, the failure canbe recovered with ease. Moreover, in the present invention, logicalconnections are controlled in group units. Thus, even if logicalconnections are controlled in a unitary manner over the entire network,the operations can be carried out with only a small number of requestsmade by connection switching exchanges and a reduced amount of control.

On top of that, the present invention provides a plurality of differentgroup sizes, and a group of detour logical connections is set up inadvance at a group size determined by one of the a group sizes providedby the invention. Thus, in the event of a failure occurring in a groupof logical connections for which a group of detour logical connectionshave been set in advance, processing to handle the failure can behandled by merely invalidating the failing group of logical connections.Even in the event of a failure occurring in a group of logicalconnections for which a group of detour logical connections have notbeen set in advance, a group of detour logical connections can be set updynamically with a group size equal to that of the failing group oflogical connections in the communication network without the need toresort to a user program on a terminating node to carry out an operationto again set up a logical connection, because all logical connections inthe communication network are controlled in group units and by usingunivocal connection identifiers. As a result, a high-reliabilitycommunication network can be built.

What is claimed is:
 1. A connection switching network control systememployed in a communication network comprising a plurality of connectionswitching exchanges and a plurality of terminating nodes connected toeach other by a plurality of communication lines wherein: a plurality oflogical communications are implemented through each of saidcommunication lines; said connection switching exchanges each comprisean exchange represented by an ATM (Asynchronous Transfer Mode) and aframe relay for switching said logical connections of said communicationlines through substitution of connection identifiers each identifyingone of said logical connections using a switching table provided in eachof said connection switching exchanges to show switching relations amongsaid logical connections; said connection switching exchanges each serveas a relay apparatus; and said terminating nodes each serve as acommunication terminal or a gateway apparatus connected to an externalnetwork, said connection switching network control system comprising anoperation-control network composed of lines different from saidcommunication lines and a network management unit which is provided insaid communication network, connected to said communication switchingexchanges in said communication network by said operation-controlnetwork and provided with grouped-connection management means as well asconnection-control information for controlling said logical connectionsin said entire communication network, wherein said grouped-connectionmanagement means: uses said operation-control network asoperation-control communication lines for communicating with saidconnection switching exchanges; puts a fixed number of said logicalconnections having consecutive connection identifiers within saidcommunication network in a plurality of group units while referring toand updating said connection-control information; controls said logicalconnections in said communication network in said group units; assigns aconnection identifier to logical connections passing through a pluralityof connection switching exchanges; and issues a command to set up orrelease logical connections in one of said group units with consecutiveconnection identifiers in said group unit to said connection switchingexchanges by way of operation-control communication lines.
 2. Aconnection switching network control system according to claim 1wherein: said network management unit is provided with storedinformation concerning a network configuration of said communicationnetwork and network-configuration-information setting means for settingup and updating said information concerning a network configurationthrough said operation-control communication line or anothercommunication line connected to said network management unit, whereinsaid information on a network configuration is composed of:connection-configuration information concerning a configuration oflogical connections among said terminating nodes and said connectionswitching exchanges constituting said communication network; initialconnection setting specifying information used for specifying initialsetting of initial logical connections; and grouped-control specifyinginformation comprising a group size specifying the size of a controlunit and group applicable range information used for specifying a rangeof connection identifiers to which control in group units is to beapplied; said connection-control information used for controlling statesof utilization, routes and attributes of said logical connections isstored in said network management unit by said grouped-connectionmanagement means employed in said network management unit in accordancewith said grouped-control specifying information stored as saidinformation on a network configuration for logical connections havingconnection identifiers specified by said group applicable rangeinformation of said grouped-control specifying information in each unitwith a size specified by said group size of said grouped-controlspecifying information; in initial setup processing to set up initiallogical connections in accordance with said initial connection settingspecifying information or in response to a request to set up a newlogical connection received from an edge connection switching exchange,that is, one of said connection switching exchanges directly connectedto one of said terminating nodes, by way of one of saidoperation-control communication lines, said grouped-connectionmanagement means: refers to said connection-control information toassign free consecutive connection identifiers or consecutive connectionidentifiers specified by said initial connection setting specifyinginformation or as specified by said request as a batch for a group oflogical connections having a size determined by said group size of saidgrouped-control specifying information; refers to saidconnection-configuration information to identify said connectionswitching exchanges on a route of a requested connection; and gives acommand to said identified connection switching exchanges by way of saidoperation-control communication lines on said route to carry outswitching in a batch operation on said group of logical connectionshaving said consecutive connection identifiers assigned above from inputcommunication lines to output communication lines on said route for bothsaid input communication lines and said output communication lines; saidconnection switching exchanges are each provided with a controlmechanism which is connected to said corresponding operation-controlcommunication line, used for controlling said connection switchingexchange and includes a connection setup/release sub-mechanism forsetting up and releasing a logical connection wherein, when said commandis received from said grouped-connection management means employed insaid network management unit, said connection setup/release mechanism:sets up said switching table in said connection switching exchange in abatch operation by using a specified group of connection identifiers soas to carry out switching on a specified group of connections withoutchanging the values of connection identifiers assigned to logicalconnections from specified input communication lines to specified outputcommunication lines; and transmits a result of said switching indicatingwhether said switching is successful or unsuccessful to saidgrouped-connection management means by way of said correspondingoperation-control communication line; and said grouped-connectionmanagement means receives said result indicating whether said switchingis successful or unsuccessful from said connection switching exchangefor updating said connection-control information accordingly.
 3. Aconnection switching network control system according to claim 1wherein, when said grouped-connection management means employed in saidnetwork management unit receives a request to release logicalconnections in a group unit by way of one of said operation-controlcommunication lines from an edge connection switching exchange, that is,one of said connection switching exchanges directly connected to one ofsaid terminating nodes, or when it is necessary to release a logicalconnection to reflect a change made to initially set up logicalconnections due to a change in configuration or to cope with theoccurrence of a failure or an abnormality, said grouped-connectionmanagement means identifies a connection switching exchange on a routeassociated with logical connections to be released by referring to saidconnection-control information and issues a command to said connectionswitching exchange on said route to release a group of logicalconnections of a group unit used in setting of said logical connectionsin a batch operation by way of one of said operation-controlcommunication lines; in said connection switching exchange receivingsaid command to release a group of logical connections, said connectionsetup/release mechanism: receives said command; releases said group oflogical connections of a specified group unit in a batch operation byclearing an entry for said specified group of logical connections insaid switching table in said connection switching exchange in a batchoperation; and transmits a result indicating whether or not saidspecified group of logical connections have been released successfullyto said grouped-connection management means employed in said networkmanagement unit by way of said operation-control communication line; andsaid grouped-connection management means receives said result indicatingwhether or not said specified group of logical connections have beenreleased successfully from said connection switching exchange and usessaid result to update said connection-control information.
 4. Aconnection switching network control system according to claim 1wherein: said grouped-connection management means employed in saidnetwork management unit handles a plurality of different group sizeswith one value being a multiple or a fraction of another and hasindividual connection-control information for each of said group sizesfor controlling logical connections in said communication network ingroup units specified by said associated group size; and when saidgrouped-connection management means gives a command to any of saidconnection switching exchanges in said communication network to requestsaid connection switching exchange to set up or release a group oflogical connections with a group size specified by said group size,processing to set up a group of logical connections having a smallergroup size is judged to be valid by being allowed to take precedence incase another group of logical connections with connection identifiersidentical with said group of logical connections to be set up orreleased have already been set up for the same communication lines ofsaid connection switching exchange.
 5. A connection switching networkcontrol system according to claim 1 wherein: said information on anetwork configuration of said network management unit includes aplurality of pieces of group control specifying information with a groupsize in one of the same plurality of pieces of group control specifyinginformation being a multiple or a fraction of a group size in anotherpiece of group control specifying information; for each piece of groupcontrol specifying information, said grouped-connection management meansemployed in said network management unit has connection-controlinformation for controlling states of utilization, connection routes andattributes of said logical connections having connection identifiers ina range specified in accordance with said group control specifyinginformation in units indicated by said group size of said group controlspecifying information; in initial setup processing to set up initiallogical connections in accordance with said initial connection settingspecifying information, in response to a request to set up a new logicalconnection received from an edge connection switching exchange, that is,one of said connection switching exchanges directly connected to one ofsaid terminating nodes, by way of one of said operation-controlcommunication lines, in response to a request to release logicalconnections of a group unit received from an edge connection switchingexchange by way of one of said operation-control communication lines orwhen it is necessary to release a logical connection to reflect a changemade to initially set up logical connections due to a change inconfiguration or to cope with the occurrence of a failure or anabnormality, said grouped-connection management means: receives acommand or request to explicitly indicates which piece of group controlspecifying information is to be used or an implicit command or requestto select which piece of group control specifying information is to beused as implicitly suggested by a relation between a specifiedconnection identifier and a piece of group control specifyinginformation to be used; and gives a command to said connection switchingexchanges on a route of said specified group of logical connections toset up or release said group of logical connections having consecutiveconnection identifiers by using a group unit specified by said groupsize of said group control specifying information selected in accordancewith said command or request as one unit by way of saidoperation-control communication lines connected to said connectionswitching exchanges; said connection setup/release mechanism employed ineach of said connection switching exchanges receiving said command toset up or release said group of logical connections sets up or releasesan entry in said switching table for switching purposes in saidconnection switching exchange in a batch operation in accordance withsaid command by using a specified group of connection identifiers so asto carry out switching on said specified group of connections tospecified communication lines; and in processing to set up logicalconnections of a plurality of group units having different group sizesbut sharing overlapping connection identifiers for the samecommunication line of one of said communication switching exchanges andin processing to release logical connections of a group unit withconnection identifiers assigned to logical connections already set up ina plurality of group units having different group sizes but sharingoverlapping connection identifiers for the same communication line ofone of said communication switching exchanges, said grouped-connectionmanagement means gives a command to said connection setup/releasemechanism employed in said connection switching exchange on saidconnection route to set up or release said logical connections so thatsetting of said logical connections sharing said overlapping connectionidentifiers in one of said group units with a smallest group size isvalid among said group units in a range of said overlapping connectionidentifiers.
 6. A connection switching network control system forcontrolling connection switching exchanges comprising an ATM and a framerelay for switching a plurality of communication lines wherein: each ofsaid connection switching exchanges has a function to set up a pluralityof logical connections in each of said communication lines forconnecting said connection switching exchange to directly connectedapparatuses, such as other connection switching exchanges, acommunication terminal or a gateway apparatus for communication withanother network, as well as a function to switch two of said logicalconnections set up in two or less communication lines connecting saidconnection switching exchange to said directly connected apparatuses;for each of said communication lines or each of said connectionswitching exchanges, there is provided individually a switching tableused for showing a relation of communication-line information on acommunication line used by a logical connection on an input side of apair of logical connections to be switched and a connection identifierassigned to said logical connection on said input side versuscommunication-line information on a communication line used by a logicalconnection on an output side of said pair of logical connections to beswitched and a connection identifier assigned to said logical connectionon said output side and used for showing optional attribute informationon attributes of said logical connections; and each of said connectionswitching exchanges comprises: a switching-table search mechanism forcarrying out a search operation to search said switching table for aswitching-table entry by using information on a connection identifierrecorded in a header of a data packet received through one of saidcommunication lines on said input side and said communication-lineinformation on said communication line and for outputting search-resultvalid/invalid information indicating whether a result of said searchoperation is valid or invalid and said switching-table entry found insaid search operation in the case of a valid result; for saidcommunication lines connected to said connection switching exchange, aconnection-identifier transformation mechanism for replacing saidconnection identifier recorded in said header of said input data packetin the case of search-result valid/invalid information indicating avalid result of said search operation carried out by saidswitching-table search mechanism with a connection identifier assignedto a logical connection on said output side toward a switchingdestination by referring to said search-result valid/invalid informationoutput by said switching-table search mechanism; a switch mechanism forswitching said data packet from said communication line on said inputside to said communication line on said output side of said switchingdestination by using said result of said search operation; a controlmechanism connected to said switch mechanism by a special signal linewherein, as part of said control mechanism, a connection setup/releasemechanism is provided for setting up said switching table through asignal line during initialization to switch to a signaling logicalconnection having a special connection identifier and for setting up anew logical connection or releasing an existing logical connection byupdating said switching table in response to a request received throughsaid signaling logical connection; a switching mask register associatedwith said switching table allowing a value received from said connectionsetup/release mechanism through a signal line to be set therein; a maskmechanism for generating a logical product (an AND value) of saidconnection identifier recorded in said header of said input data packetand contents of said switching mask register and supplying said logicalproduct to said switching-table search mechanism for use in said searchoperation to search said switching table instead of directly supplyingsaid connection identifier recorded in said header of said input datapacket to said switching-table search mechanism; andswitching-information transformation mechanism for computing a logicalproduct of said connection identifier of said input data packet and avalue resulting from bit-by-bit inversion of contents of saidswitching-mask register and generating a logical sum (an OR value) ofsaid logical product and an output connection identifier included insaid switching-table entry obtained as a result of said search operationcarried out by said switching-table search mechanism, wherein saidlogical sum output by said switching-information transformationmechanism is used as a new search result supplied to saidconnection-identifier transformation mechanism and, if saidsearch-result valid/invalid information indicates a valid search result,said connection identifier included in said input data packet isreplaced in said connection-identifier transformation mechanism, andsaid switch mechanism carries out switching on said input data packetcompleting processing in said connection-identifier transformationmechanism from said communication line on said input side to saidcommunication line on said output side of a switching destination byusing information on an output communication line of said search result.7. A connection switching network control system according to claim 6wherein: each of said connection switching exchanges has: a plurality ofgrouped-search mechanisms each comprising said switching table, saidswitching mask register, said mask mechanism and saidswitching-information transformation mechanism wherein said switchingtables are searched at the same time and search results are supplied tosaid switching-information transformation mechanisms to be subjected totransformations; and a priority judgment/selection mechanism receivingswitching-table entries of said search results obtained from saidtransformations carried out by said switching-information transformationmechanisms employed in said grouped-search mechanisms and pieces ofsearch-result valid/invalid information from said switching-table searchmechanisms employed in said grouped-search mechanisms each associatedwith one of said switching-table entries, wherein said switching-tableentries each indicated to be a valid search result by said associatedsearch-result valid/invalid information are subjected to a priorityjudgment wherein fixed different priority levels are assigned in advanceto said grouped-search mechanisms or a priority judgment comprising thesteps of: inputting contents of said switching mask registers employedin said grouped-search mechanisms; treating each of said values as anunsigned integer; judging one of said switching-table entries of saidsearch results associated with a greatest one among said unsignedintegers to be a switching-table entry output by one of saidgrouped-search mechanisms with a highest priority level; and selectingsaid switching-table entry with said highest priority level among saidswitching-table entries output by the same plurality of saidgrouped-search mechanisms each indicated to be a valid search result bysaid associated search-result valid/invalid information, and outputtingsaid selected switching-table entry as a final search result along withfinal search-result valid/invalid information obtained as a logical sum(an OR value) of all said pieces of search-result valid/invalidinformation for indicating whether said final search result is valid orinvalid; said final search result and said final search-resultvalid/invalid information output by said priority judgment/selectionmechanism are supplied to said connection-identifier transformationmechanism as a new search result and new search-result valid/invalidinformation in which said connection identifier included in said inputdata packet is replaced provided that said new search-resultvalid/invalid information indicates that said new search result is validand said switch mechanism carries out switching of said input datapacket completing processing in said connection-identifiertransformation mechanism from said communication line on said input sideto said communication line on said output side for said switchingdestination by using information on an output communication linerecorded in said switching-table entry of said new search result.
 8. Aconnection switching network control system according to claim 6 forcontrolling connection switching exchanges composing a communicationnetwork as in claim 1 wherein group units can each be set only to aninteger value in power of 2 and, in initialization, saidgrouped-connection management means employed in said network managementunit: gives a command to said connection setup/release mechanism of eachof said connection switching exchanges in said communication network byway of said operation-control communication lines to request saidconnection setup/release mechanisms of said connection switchingexchanges to set a value obtained as a result of bit-by-bit inversion of(a group size-1) in said switching mask register employed in each ofsaid grouped-search mechanisms to which said group size is assignedconsidering smaller group size is assigned to a grouped-search mechanismwith higher priority if fixed priority levels are pre-assigned to saidgrouped-search mechanisms; waits for responses indicating completion ofsaid initialization coming from said connection switching exchanges; andstores a relation between group units completing said initialization andsaid switching tables of said grouped-search mechanisms in saidconnection-control information for said group units as informationassociating said group units with said switching tables, and after saidinitialization, referring to said information associating said groupunits with said switching tables stored as part of saidconnection-control information at the end of said initialization, saidgrouped-connection management means employed in said network managementunit gives a command to said connection setup/release mechanism employedin each of said connection switching exchanges to carry out processingto set up or release a group of logical connections for a group unit byspecification of one of said grouped-search mechanisms with saidswitching table thereof to be used; and said connection setup/releasemechanism employed in said connection switching exchange updates anentry in said switching table of said specified grouped-search mechanismin said connection switching exchange in order to set up or release aspecified group of logical connections in accordance with said command.9. A connection switching network control method to be adopted in anetwork management unit including a grouped-connection management meansaccording to claim 4 for controlling conventional connection switchingexchanges composing a communication network wherein neithergrouped-search mechanism nor priority judgment/selection mechanism areincluded in each of said conventional connection switching exchanges,whereby an operation to issue a command to set up or release logicalconnections carried out by said grouped-connection management meansemployed in said network management unit comprises: a step 0 at whichsaid grouped-connection management means employed in said networkmanagement unit, first of all, uses values of an entireconnection-identifier space as a range when setting up logicalconnections initially in initialization and values of a group ofconnection identifiers of logical connections to be set up or releasedas a range when setting up or releasing said logical connections aftersaid initialization, then end points of said range and start and endconnection identifiers of all grouped logical connections in said rangewhich have been set up or will be set up from now on as change pointsare considered as change points, and said change points are sorted in anincreasing order of change-point values to form a list of change points;step 1 at which a group size of a request to set up or release logicalconnections is stored as an affected group size; step 2 at which logicalconnections having a connection identifier of a change point at thestart side of said range are searched and, if such logical connectionsexist, said change point is stored as a set start point and a smallestgroup size among found logical connections is stored as a setting groupsize before going on to a step 4 but, if a logical connection having aconnection identifier of a change point is not found, on the other hand,the value of a change point on said start side is stored as a set endpoint; step 3 at which a next change point which follows said set endpoint in said change-point list and has a value different from said setend point is stored as a set start point, in the case of a request torelease logical connections, a command to release a group of logicalconnections having connection identifiers from said set end point tosaid set start point is given to said connection switching exchanges ona route of said logical connections to be released and a smallest groupsize among logical connections having said set start point cited abovein connection identifiers thereof is stored as a setting group size;step 4 at which change points on said change-point list following saidset start point are sequentially checked to search for a smallest changepoint where a group unit size of a logical connection having aconnection identifier thereof is not greater than said setting groupsize, or which is an end point of a group of logical connectionscorresponding to said set start point; step 5 at which said affectedgroup size stored at step 1 is compared with a group size set previouslyand, in the case where an affected group size is equal to or smallerthan said previously set group size and the processing is to set uplogical connections, a command to set up logical connections from saidset start point to said change point obtained at step 4 is issued toassociated connection switching exchanges but, in the case where anaffected group size is greater than said previously set group size andthe processing is to release logical connections, on the other hand, acommand to set up logical connections from said set start point to saidchange point is issued to associated connection switching exchanges; andstep 6 at which said change point obtained at step 4 is checked to findout whether or not said change point is a last change point on saidchange-point list and, if said point is a last change point, processingis ended but, if said change point is judged to be not a last changepoint, on the other hand, a logical connection having said change pointin a connection identifier thereof is searched for and, if such logicalconnections are found, said change point is stored as a set start pointand a smallest group size among found logical connections is stored as asetting group size before returning to step 4 but, if a logicalconnection having said change point obtained at step 4 in a connectionidentifier thereof is not found, on the other hand, said change point isstored as a set end point before returning to step
 3. 10. A connectionswitching network control system according to claim 4 wherein, whenswitching setting of a group of logical connections with a sizespecified by said group size is established for a communication line ofa connection switching exchange, switching setting of another group oflogical connections with another group size larger than said group sizeis established at the same time to include connection identifiers ofsaid group of logical connections for the same communication line of thesame connection switching exchange.
 11. A connection switching networkcontrol system according to claim 4 wherein a group of logicalconnections of a group unit linked to a communication switching exchangeis distributed among a plurality of subgroups of logical connectionswith a subgroup size equal to a fraction of a group size of said groupunit and a total number of logical connections in all said subgroupssmaller than the number of logical connections in said group unit, andremaining logical connections not distributed to said subgroups arecontrolled as spare logical connections.
 12. A connection switchingnetwork control system according to claim 1 wherein: all apparatus insaid communication network are classified into hierarchical categorieswherein terminating nodes are put in a category of level-0 apparatuses,edge connection switching exchanges each directly connected to aterminating node are put in a category of level-1 apparatuses,connection switching exchanges each directly connected to a level-1apparatus but not pertaining to said categories of level-1 apparatusesand level-0 apparatuses are put in a category of level-2 apparatusesand, by the same token, connection switching exchanges each directlyconnected to a level-(n−1) apparatus but not pertaining to categories oflevel-(n−1) apparatuses and numerically-lower-than-(n−1)-levelapparatuses are put in a category of level-n apparatuses, and aone-directional interterminal logical connection is set between everytwo level-0 apparatuses; each one-directional interterminal logicalconnection has a connection identifier unique to a destinationterminating node so that one-directional interterminal logicalconnections from terminating nodes to the same destination terminatingnode all have the same connection identifier, forming a so-calledmultipoint-to-point logical connections; for apparatuses at allhierarchical levels i where i>=1, one-directional interterminal logicalconnections from an apparatus at level i to apparatuses at level (i−1)have consecutive connection identifiers; for anticipated futureexpansion of apparatus connections, a proper number of connectionidentifiers are reserved for apparatuses at level i; the total number ofone-directional interterminal logical connections from an apparatus atlevel i to apparatuses at level (i−1) including said reserved ones is amultiple of a group unit size and connection identifiers of logicalconnections toward apparatuses at level (i−1) and reserved connectionidentifiers are assigned in said group unit; a group of logicalconnections having connection identifiers assigned in said group unitare set in said group unit from all apparatuses at level (i+1) directlyconnected to said apparatus at level i to said apparatus at level i; ata connection switching exchange at level i, a group of logicalconnections from apparatuses at level (i+1) to an apparatus at level iare distributed to be connected to logical connections or a group oflogical connections from said apparatus at level i to apparatuses atlevel i−1; and one-directional logical connections using logicalconnections in group units from a high hierarchical layer to a lowhierarchical layer set as described above are connected from eachterminating node to form meshed interterminal connections withone-directional logical connections having group unit size equal to orgreater than that of said one-directional logical connections to beconnected to.
 13. A connection switching network control systemaccording to claim 12 wherein the level of each apparatus is virtuallylowered by 1 layer with apparatuses at level 1 each considered to be aterminating node and one-directional logical connections stretched amongedge connection switching exchanges are set up in place of saidone-directional interterminal logical connections.
 14. A connectionswitching network control system according to claim 12 wherein: eachterminating node or each edge connection switching exchange directlyconnected to a terminating node in said communication network isprovided with IP/connection transformation information for indicatingwhich one-directional interterminal logical connection is to be used intransmission of IP data and which apparatus or apparatuses correspond toan IP/(Internet Protocol) address or a group of IP addresses in said IPdata; and each terminating node or each edge connection switchingexchange transmits IP data through a one-directional interterminallogical connection indicated by said IP/connection transformationinformation.
 15. A connection switching network control system accordingto claim 12 wherein: said network management unit is provided withIP-route information showing which terminating node or nodes adestination IP address or a group of destination IP addresses includedin IP data indicate, that is, which terminating node or nodes said IPdata with a destination IP address or a group of destination IPaddresses should be transmitted to, or which terminating node or nodesIP data should be transmitted through; said grouped-connectionmanagement means employed in said network management unit createsIP/connection transformation information for transforming an IP addressor a group of IP addresses into connection identifiers ofone-directional interterminal logical connections toward destinationterminating nodes set up among terminating nodes during initializationby using said IP-route information and said connection-controlinformation; said grouped-connection management means employed in saidnetwork management unit transmits said IP/connection transformationinformation to said edge connection switching exchange directlyconnected to said terminating node through said operation-controlcommunication line; said edge connection switching exchange receivessaid IP/connection transformation information and stores saidIP/connection transformation information; said edge connection switchingexchanges each have an IP/connection transformation mechanism as part ofsaid control mechanism; said IP/connection transformation mechanism isconnected to said terminating nodes to which said edge connectionswitching exchange is linked directly by using IP logical connectionshaving pre-configured IP connection identifiers; any of said terminatingnodes transmits IP data to said edge connection switching exchange byusing said logical connections; receiving said IP data from saidterminating node, said IP/connection transformation mechanism employedin said edge connection switching exchange uses a destination IP addressrecorded in an IP header of said IP data received from said terminatingnode as a key to search said IP/connection information stored in saidedge connection switching exchange for a connection identifier of aone-directional interterminal logical connection toward a destinationterminating node; and by using said one-directional interterminallogical connection, said IP data is transmitted by said edge connectionswitching exchange to said destination terminating node.
 16. Aconnection switching network control system according to claim 12wherein: said network management unit is provided with IP-routeinformation showing which terminating node or nodes a destination IPaddress or a group of destination IP addresses included in IP dataindicate, that is, which terminating node or nodes said IP data with adestination IP address or a group of destination IP addresses should betransmitted to, or which terminating node or nodes IP data should betransmitted through; said grouped-connection management means employedin said network management unit creates IP/connection transformationinformation for transforming an IP address or a group of IP addressesinto connection identifiers of one-directional interterminal logicalconnections toward destination terminating nodes set up amongterminating nodes during initialization by using said IP-routeinformation and said connection-control information; saidgrouped-connection management means employed in said network managementunit transmits said IP/connection transformation information to saidedge connection switching exchange directly connected to saidterminating node through said operation-control communication line; saidedge connection switching exchange receives said IP/connectiontransformation information and stores said IP/connection transformationinformation; said edge connection switching exchanges each have anIP/connection transformation mechanism as part of said controlmechanism; said IP/connection transformation mechanism is connected tosaid terminating nodes to which said edge connection switching exchangeis linked directly by using IP logical connections having different IPconnection identifiers; each of said terminating nodes is provided withan IP/connection transformation cache for storing some of saidIP/connection transformation information used for transforming adestination IP address of IP data transmitted in the past into anidentifier of a one-directional interterminal connection to adestination; first of all, said terminating node searches saidIP/connection transformation cache prior to transmission of IP data inorder to form a judgment as to whether or not an entry corresponding toa destination IP address included in said IP data exists in said cacheand if such an entry does not exist in said IP/connection transformationcache, said terminating node transmits information on said destinationIP address to said IP/connection transformation mechanism employed insaid edge connection switching exchange directly connected to saidterminating node by using said IP logical connection in order to obtainIP/connection transformation information; receiving said information onsaid destination IP address, said IP/connection transformation mechanismemployed in said edge connection switching exchange searches saidIP/connection transformation information stored in said edge connectionswitching exchange for a desired portion associated with saiddestination IP address, transmitting said desired portion of saidIP/connection transformation information to said terminating nodeoriginating said IP address as a result of said search operation;receiving said result, said terminating node stores said desired portionof said IP/connection transformation information received in response tosaid destination IP address in said IP/connection transformation cache;and said terminating node finds a connection identifier of aone-directional interterminal logical connection corresponding to saiddestination IP address from said cataloged IP/connection transformationinformation and then transmits said IP data to said edge connectionswitching exchange directly connected to said terminating node by usingsaid connection identifier of said one-directional interterminal logicalconnection.
 17. A connection switching network control system accordingto claim 16 wherein: said IP/connection transformation cache employed insaid terminating node is used for storing said entire IP/connectiontransformation information transmitted from said edge connectionswitching exchange instead of storing only part of said IP/connectiontransformation information when said edge connection switching exchangereceives said IP/connection transformation information from saidgrouped-connection management means employed in said network managementunit and passes on said IP/connection transformation information to allsaid terminating nodes by using said IP connection, or when saidterminating node makes a request to said edge connection switchingexchange to transmit said entire IP/connection transformationinformation by using said IP connection; and in transmission of IP data,said terminating node finds a connection identifier of a one-directionalinterterminal logical connection corresponding to a destination IPaddress of said IP data from said IP/connection transformationinformation stored entirely in said terminating node and then transmitssaid IP data to said edge connection switching exchange directlyconnected to said terminating node by using said connection identifierof said one-directional interterminal logical connection.
 18. Aconnection switching network control system according to claim 13wherein each of edge connection switching exchanges of saidcommunication network is provided with:IP/inter-edge-exchange-connection transformation information fortransforming an IP address or a group of IP addresses of IP data intoconnection identifiers of one-directional inter-edge-exchange logicalconnections to be used for transmitting said IP data; andIP/terminal-line transformation information for transforming adestination edge connection switching exchange or a destination edgeconnection switching exchanges corresponding respectively to an IPaddress or a group of IP addresses of said IP data into informationindicating which communication line connected to a terminating node saidIP data should be transmitted through in order to transmit said IP datato an apparatus or apparatuses indicated by said IP address or IPaddresses respectively from an edge connection switching exchange, andin said edge communication switching exchange, saidIP/inter-edge-exchange-connection transformation information andIP/terminal-line transformation information are used to transmit IP datathrough said one-directional inter-edge-exchange logical connections.19. A connection switching network control method adopted in aconnection switching network control system according to claim 13wherein: said network management unit is provided with IP-routeinformation showing which terminating node or nodes IP data with an IPaddress or a group of IP addresses respectively should be transmitted toand which edge connection-switching exchange or switching exchanges IPdata should be transmitted through or which terminating node or nodesand which edge connection-switching exchange or switching exchanges IPdata should be transmitted through; each of said edge connectionswitching exchanges is provided with an IP/connection transformationmechanism and an IP/terminal-line transformation mechanism as part ofsaid control mechanism; an inter-edge-exchange one-directional logicalconnection toward a destination edge connection switching exchange setup during said initialization is connected to said IP/terminal-linetransformation mechanism; and said IP/connection transformationmechanism is connected to a source terminating node directly connectedto said edge connection switching exchange by an IP transmission logicalconnection having an IP connection identifier and said IP/terminal-linetransformation mechanism is connected to a destination terminating nodedirectly connected to said edge connection switching exchange by an IPreception logical connection having an IP connection identifier; saidmethod comprising: a step taken by said grouped-connection managementmeans employed in said network management unit to createIP/inter-edge-exchange-connection transformation information fortransforming an IP address or a group of IP addresses of IP data intoconnection identifiers of one-directional inter-edge-exchange logicalconnections toward destination edge connection switching exchanges whichwere set up among terminating nodes during said initialization by usingsaid IP-route information and said connection-control information; astep taken by said grouped-connection management means employed in saidnetwork management unit to create IP/terminal-line transformationinformation used for transforming information on a destination edgeconnection switching exchange included in IP data into informationindicating which terminating node and which communication line IP datashould be transmitted to and transmitted through by using said IP-routeinformation and said connection-configuration information for an IPaddress or a group of IP addresses of said IP data; a step taken by saidgrouped-connection management means employed in said network managementunit to transmit said IP/inter-edge-exchange-connection transformationinformation and said IP/terminal-line transformation information to saidedge connection switching exchanges directly connected to saidterminating nodes through said operation-control communication lines; astep taken by said edge connection switching exchanges to receive saidIP/inter-edge-exchange-connection transformation information and saidIP/terminal-line transformation information and store saidIP/inter-edge-exchange-connection transformation information and saidIP/terminal-line transformation information; a step taken by aterminating node to transmit IP data to an edge connection switchingexchange by using said IP transmission logical connection; a step takenby said IP/connection transformation mechanism employed in said edgeconnection switching exchange receiving said IP data from saidterminating node to use a destination IP address recorded in an IPheader of said IP data received from said terminating node as a key tosearch said IP/inter-edge-exchange connection transformation informationstored in said edge connection switching exchange for a connectionidentifier of a one-directional inter-edge-exchange logical connectiontoward a destination edge connection switching exchange to transmit saidIP data to said destination edge connection switching exchange by usingsaid one-directional inter-edge-exchange logical connection; and a steptaken by said IP/terminal-line transformation mechanism employed in saiddestination edge connection switching exchange to receive said IP datatransmitted by said source edge connection switching exchange throughsaid one-directional inter-edge-exchange logical connection and, byreferring to said IP/terminal-line transformation information, to passon said IP data to said terminating node connected to said communicationline for said IP data through said IP reception logical connection. 20.A connection switching network control method adopted in a connectionswitching network control system according to claim 1 wherein saidconnection setup/release mechanism employed in each edge connectionswitching exchange directly connected to one of said terminating nodesserves as a buffer for requests to set up a logical connection made bysaid terminating node, makes the requests into setting of a group oflogical connections in a new connection setting unit which is a multipleof a group size, and, for each group of logical connections dynamicallyset, said connection setup/release mechanism hasterminal-connection-control information on said group of logicalconnections and on the status of assignment of the logical connectionsto said terminating nodes, said method comprising: a step taken by saidterminating node to issue a request to set up a new logical connectionto an edge connection switching exchange through a signaling logicalconnection; a step taken by said connection setup/release mechanism ofsaid edge connection switching exchange receiving said request to checkpieces of said terminal-connection-control information in order tosearch for terminal-connection-control information with destination andattribute conditions satisfying said request; a step taken by saidconnection setup/release mechanism of said edge connection switchingexchange to request said grouped-connection management means employed insaid network management unit to set up a group of logical connections insaid new connection setting unit size from said edge connectionswitching exchange to a destination apparatus with requested attributesspecified in said request by using a method adopted by said connectionswitching network control system according to claim 1, and catalog saidgroup of logical connections obtained from said grouped-connectionmanagement means in said terminal-connection-control information asunassigned logical connections if terminal-connection-controlinformation meeting said conditions is not found; a step taken by saidconnection setup/release mechanism of said edge connection switchingexchange to select as many logical connections as requested from saidfound terminal-connection-control information orterminal-connection-control information cataloged at said above step byusing said terminal-connection-control information and to update saidterminal-connection-control information if terminal-connection-controlinformation meeting said conditions is found; a step taken by saidconnection setup/release mechanism of said edge connection switchingexchange to set up said switching table to link said logical connectionselected at said above step starting from said edge connection switchingexchange and ending at said destination to said terminating node, whichmade said request, by using said same connection identifier as saidlogical connection; and a step taken by said connection setup/releasemechanism to report said set connection identifier to said terminatingnode which made said request.
 21. A connection switching network controlmethod according to claim 20 wherein said terminal-connection-controlinformation includes time-out information used for releasing a group oflogical connections, said method composed of: a sequence of steps torelease a logical connection comprising: a step taken by a terminatingnode to issue a request to release a logical connection to an edgeconnection switching exchange directly connected to said terminatingnode through a signaling logical connection; a step taken by saidconnection setup/release mechanism of said edge connection switchingexchange receiving said request to search forterminal-connection-control information for said logical connectionbeing released by using a connection identifier specified in saidrequest; a step taken by said connection setup/release mechanism toupdate said terminal-connection-control information found at said abovestep by changing status of assignment of said logical connection beingreleased connected to terminating nodes into an unassigned one; a steptaken by said connection setup/release mechanism to invalidate an entryin said switching table in said edge connection switching exchangecorresponding to said logical connection being released; and a steptaken by said connection setup/release mechanism to set said time-outinformation in said found terminal-connection-control information forreleasing all logical connections in a group with a size equal to thesize of said new connection setting unit associated with saidterminal-connection-control information in case status of assignments ofall said logical connections is unassigned status, and a sequence ofsteps executed by said connection setup/release mechanism toperiodically check said time-out information of saidterminal-connection-control information with a group of logicalconnections associated with said terminal-connection-control informationhaving unassigned status, said sequence comprising the steps of:requesting said grouped-connection management means employed in saidnetwork control means through an operation-control communication line torelease a group of unassigned logical connections associated with saidterminal-connection-control information with a group size equal to thesize of said new logical connection unit if said time-out information ofsaid terminal-connection-control information set at said above stepindicates that said unassigned status of a group of logical connectionsassociated with said terminal-connection-control information has beencontinuing for more than a predetermined period of time; and deletingsaid terminal-connection-control information.
 22. A connection switchingnetwork control method adopted in a connection switching network controlsystem according to claim 1 for handling a failure occurring in saidcommunication network wherein: a plurality of different group sizes areused; a group of detour logical connections are provided in advance fora group of normal-route logical connections; the size of said group ofdetour logical connections is larger than the size of said group ofnormal-route logical connections; and connection identifiers used insaid group of normal-route logical connections are used as connectionidentifiers in said group of detour logical connections, said methodcomprising the steps taken by said grouped-connection management meansemployed in said network management unit to: identify a failing group oflogical connections and a failing route affected by said failure byreferring to said connection-control information and saidconnection-configuration information stored in said network managementunit; examine whether or not a group of detour logical connections forsaid failing group of logical connections with a group size greater thanthe group size of said failing group of logical connections have alreadybeen set up by referring to said connection-control information; give acommand to said connection switching exchanges on said failing routethrough said operation-control communication lines to invalidateconnection switching for said failing group of logical connections ifsuch a group of detour logical connections have already been set up; andupdate said connection-control information to reflect said invalidatedconnection switching.
 23. A connection switching network control methodadopted in a connection switching network control system according toclaim 1 for handling a failure occurring in said communication network,said method comprising the steps taken by said grouped-connectionmanagement means employed in said network management unit to: identify afailing group of logical connections and a failing route affected bysaid failure by referring to said connection-control information andsaid connection-configuration information stored in said networkmanagement unit; and examine whether or not a group of detour logicalconnections for said failing group of logical connections with a groupsize greater than the group size of said failing group of logicalconnections have already been set up by referring to saidconnection-control information and if a result of examination indicatesthat a group of detour logical connections have not been set up then:determine a detour route by referring to said connection-controlinformation and said connection-configuration information; form ajudgment based on consideration of conditions such as a band as towhether said connection identifiers of said failing group of logicalconnections are to be used as they are as connection identifiers of agroup of detour logical connections or other connection identifiers areto be assigned to said group of detour logical connections and, ifnecessary, assign new connection identifiers to said group of detourlogical connections; give a command to connection switching exchanges atlocations on said detour route determined at said above step by way ofsaid operation-control communication lines to carry out connectionswitching on said group of logical connections having said detourconnection identifiers with a group size equal to that of said failinggroup of logical connections; give a command to a connection switchingexchange or a terminating node at an end on the source side of saiddetour route to carry out connection switching to link a group of alogical connections connected to said failing group of logicalconnections to said group of detour logical connections switched by saidconnection switching exchanges at locations on said detour route with agroup size equal to that of said failing group of logical connectionswith any one of the ends of said detour route regarded as a source inthe case of a failing group of logical connections composed ofbi-directional logical connections after completion of said above stepto switch a group of detour logical connections for said connectionswitching exchanges at locations on said detour route; give a command toa connection switching exchange or a terminating node at an end on thedestination side of said detour route to carry out connection switchingto link a group of a logical connections connected to said failing groupof logical connections to said group of detour logical connectionsswitched by said connection switching exchanges at locations on saiddetour route with a group size equal to that of said failing group oflogical connections after completion of said above step to switchlogical connections in said connection switching exchange or saidterminating node at said end on said source side of said detour route;and update said connection-control information to reflect said settingof said detour route.
 24. A connection switching network control methodadopted in a connection switching network control system according toclaim 1 wherein: said network management unit is connected bycommunication lines using operation-control logical connections eachhaving a connection identifier directly to said communication networkincluding connection switching exchanges serving as relay apparatuses inthe same way as said terminating nodes and said connection switchingexchanges are connected to said communication network; and saidcommunication lines using said operation-control logical connections areeach used as an operation-control communication line of saidcommunication network.
 25. A connection switching network control systemwherein: a connection setup/release mechanism serving as a controlmechanism according to claim 2, an IP/connection transformationmechanism according to claim 15 and an IP/terminal-line transformationmechanism according to claim 19 are provided for each of saidcommunication lines in each of said connection switching exchanges; andthere is provided a logical connection distribution mechanism forcontrolling distribution of logical connections to sub-mechanisms insaid control mechanism for handling only data packets of logicalconnections toward said control mechanism.
 26. A connection switchingnetwork control system according to 1 wherein: the plurality of networkmanagement units are provided in said communication network;connection-control information according to claim 1 subjected to unitarycontrol across said entire communication network is provided in each ofsaid network management units by adopting the same technique as adistributed data base in a cache subjected to control of consistencyamong said network management units; and processing is distributed amongthe same plurality of network management units according to ranges ofdistribution of connection identifiers and ranges of distribution ofconnection switching exchanges.